improve test in the planner/casetest

## Enhancement

when you run test cases in the remote execution, Here is a simple report about these test cases.

```
INFO: Elapsed time: 676.260s, Critical Path: 548.74s
INFO: 9636 processes: 4269 disk cache hit, 5368 remote.
INFO: Build completed successfully, 9636 total actions
Test cases: finished with 0 passing and 0 failing out of 0 test cases

Executed 282 out of 282 tests: 282 tests pass.
There were tests whose specified size is too big. Use the --test_verbose_timeout_warnings command line option to see which ones these are.
```

If we dump the detail report. we can read this.

```
WARNING: This information is intended for consumption by Bazel developers only, and may change at any time. Script against it at your own risk
INFO: Profile created on Sat May 06 13:07:34 CST 2023, build ID: bf8e4e04-71bc-45a2-8904-457b634ff6a0, output base: /data2/root/.cache/bazel/_bazel_root/6a98a1fb5f5da1c9e5bd87d2f46d0229

=== PHASE SUMMARY INFORMATION ===

Total launch phase time 4.687 s 0.69%
Total init phase time 7.030 s 1.04%
Total target pattern evaluation phase time 0.000 s 0.00%
Total interleaved loading-and-analysis phase time 10.295 s 1.52%
Total preparation phase time 24.986 s 3.69%
Total execution phase time 629.260 s 93.04%
Total finish phase time 0.062 s 0.01%
---------------------------------------------------------------------
Total run time 676.322 s 100.00%

Critical path (548.744 s):
Time Percentage Description
32.7 ms 0.01% action 'GoToolchainBinaryBuild external/go_sdk/builder [for tool]'
230 ms 0.04% action 'Creating symlink bazel-out/k8-opt-exec-2B5CBBC6-ST-e4bf93cdf86e/bin/external/go_sdk/builder_reset/builder [for tool]'
5.349 s 0.97% action 'GoStdlib external/io_bazel_rules_go/stdlib_/pkg [for tool]'
424 ms 0.08% action 'GoCompilePkg external/org_golang_x_tools/internal/typeparams/typeparams.a [for tool]'
840 ms 0.15% action 'GoCompilePkg external/org_golang_x_tools/go/ast/astutil/astutil.a [for tool]'
47.0 ms 0.01% action 'GoCompilePkg external/org_golang_x_tools/go/types/typeutil/typeutil.a [for tool]'
215 ms 0.04% action 'GoCompilePkg external/co_honnef_go_tools/go/types/typeutil/typeutil.a [for tool]'
138 ms 0.03% action 'GoCompilePkg external/co_honnef_go_tools/go/ir/ir.a [for tool]'
56.5 ms 0.01% action 'GoCompilePkg external/co_honnef_go_tools/internal/passes/buildir/buildir.a [for tool]'
145 ms 0.03% action 'GoCompilePkg external/co_honnef_go_tools/analysis/facts/purity/purity.a [for tool]'
10.2 ms 0.00% action 'GoCompilePkg external/co_honnef_go_tools/analysis/code/code.a [for tool]'
22.0 ms 0.00% action 'GoCompilePkg external/co_honnef_go_tools/internal/sharedcheck/sharedcheck.a [for tool]'
45.2 ms 0.01% action 'GoCompilePkg external/co_honnef_go_tools/simple/simple.a [for tool]'
53.9 ms 0.01% action 'GoCompilePkg build/linter/staticcheck/S1018.a [for tool]'
64.0 ms 0.01% action 'GoCompilePkg build/tidb_nogo_actual~nogo.a [for tool]'
238 ms 0.04% action 'GoLink build/tidb_nogo_actual_/tidb_nogo_actual [for tool]'
33.1 ms 0.01% action 'GoCompilePkg external/org_golang_google_protobuf/internal/detrand/detrand.a'
840 ms 0.15% action 'GoCompilePkg external/org_golang_google_protobuf/internal/errors/errors.a'
667 ms 0.12% action 'GoCompilePkg external/org_golang_google_protobuf/encoding/protowire/protowire.a'
1.510 s 0.28% action 'GoCompilePkg external/org_golang_google_protobuf/reflect/protoreflect/protoreflect.a'
776 ms 0.14% action 'GoCompilePkg external/org_golang_google_protobuf/internal/strs/strs.a'
970 ms 0.18% action 'GoCompilePkg external/org_golang_google_protobuf/internal/encoding/text/text.a'
1.830 s 0.33% action 'GoCompilePkg external/org_golang_google_protobuf/internal/encoding/defval/defval.a'
1.281 s 0.23% action 'GoCompilePkg external/org_golang_google_protobuf/internal/filedesc/filedesc.a'
3.709 s 0.68% action 'GoCompilePkg external/org_golang_google_protobuf/internal/encoding/tag/tag.a'
6.915 s 1.26% action 'GoCompilePkg external/org_golang_google_protobuf/internal/impl/impl.a'
552 ms 0.10% action 'GoCompilePkg external/org_golang_google_protobuf/internal/filetype/filetype.a'
774 ms 0.14% action 'GoCompilePkg external/org_golang_google_protobuf/runtime/protoimpl/protoimpl.a'
2.939 s 0.54% action 'GoCompilePkg external/org_golang_google_protobuf/types/known/durationpb/durationpb.a'
430 ms 0.08% action 'GoCompilePkg external/com_github_golang_protobuf/ptypes/duration/duration.a'
18.5 ms 0.00% action 'GoCompilePkg external/com_github_golang_protobuf/ptypes/ptypes.a'
575 ms 0.10% action 'GoCompilePkg external/org_golang_google_grpc/internal/status/status.a'
56.3 ms 0.01% action 'GoCompilePkg external/org_golang_google_grpc/status/status.a'
50.9 ms 0.01% action 'GoCompilePkg external/org_golang_google_grpc/internal/binarylog/binarylog.a'
53.1 ms 0.01% action 'GoCompilePkg external/org_golang_google_grpc/grpc.a'
123 ms 0.02% action 'GoCompilePkg external/com_github_pingcap_kvproto/pkg/resource_manager/resource_manager.a'
338 ms 0.06% action 'GoCompilePkg external/com_github_pingcap_kvproto/pkg/kvrpcpb/kvrpcpb.a'
111 ms 0.02% action 'GoCompilePkg external/com_github_pingcap_kvproto/pkg/raft_serverpb/raft_serverpb.a'
175 ms 0.03% action 'GoCompilePkg external/com_github_pingcap_kvproto/pkg/pdpb/pdpb.a'
88.5 ms 0.02% action 'GoCompilePkg external/com_github_pingcap_kvproto/pkg/tsopb/tsopb.a'
56.8 ms 0.01% action 'GoCompilePkg external/com_github_tikv_pd_client/client.a'
18.6 ms 0.00% action 'GoCompilePkg external/com_github_tikv_client_go_v2/util/util.a'
22.3 ms 0.00% action 'GoCompilePkg external/com_github_tikv_client_go_v2/error/error.a'
17.6 ms 0.00% action 'GoCompilePkg external/com_github_tikv_client_go_v2/kv/kv.a'
85.4 ms 0.02% action 'GoCompilePkg external/com_github_tikv_client_go_v2/tikvrpc/tikvrpc.a'
68.8 ms 0.01% action 'GoCompilePkg util/resourcegrouptag/resourcegrouptag.a'
729 ms 0.13% action 'GoCompilePkg sessionctx/stmtctx/stmtctx.a'
3.235 s 0.59% action 'GoCompilePkg types/types.a'
370 ms 0.07% action 'GoCompilePkg util/chunk/chunk.a'
356 ms 0.06% action 'GoCompilePkg util/codec/codec.a'
1.047 s 0.19% action 'GoCompilePkg kv/kv.a'
884 ms 0.16% action 'GoCompilePkg structure/structure.a'
1.023 s 0.19% action 'GoCompilePkg meta/meta.a'
970 ms 0.18% action 'GoCompilePkg meta/autoid/autoid.a'
1.548 s 0.28% action 'GoCompilePkg util/tableutil/tableutil.a'
3.874 s 0.71% action 'GoCompilePkg sessionctx/variable/variable.a'
2.523 s 0.46% action 'GoCompilePkg extension/extension.a'
34.4 ms 0.01% action 'GoCompilePkg sessionctx/sessionctx.a'
2.214 s 0.40% action 'GoCompilePkg util/sqlexec/sqlexec.a'
1.518 s 0.28% action 'GoCompilePkg util/mock/mock.a'
40.246 s 7.33% action 'GoCompilePkg expression/expression.a'
5.179 s 0.94% action 'GoCompilePkg util/ranger/ranger.a'
81.6 ms 0.01% action 'GoCompilePkg planner/util/util.a'
1.608 s 0.29% action 'GoCompilePkg statistics/statistics.a'
4.522 s 0.82% action 'GoCompilePkg table/tables/tables.a'
2.368 s 0.43% action 'GoCompilePkg infoschema/infoschema.a'
263 ms 0.05% action 'GoCompilePkg sessiontxn/sessiontxn.a'
129 ms 0.02% action 'GoCompilePkg statistics/handle/handle.a'
341 ms 0.06% action 'GoCompilePkg br/pkg/metautil/metautil.a'
2.298 s 0.42% action 'GoCompilePkg br/pkg/utils/utils.a'
1.774 s 0.32% action 'GoCompilePkg br/pkg/lightning/common/common.a'
946 ms 0.17% action 'GoCompilePkg br/pkg/lightning/verification/verification.a'
1.858 s 0.34% action 'GoCompilePkg br/pkg/lightning/backend/encode/encode.a'
1.903 s 0.35% action 'GoCompilePkg br/pkg/lightning/backend/kv/kv.a'
794 ms 0.14% action 'GoCompilePkg br/pkg/lightning/backend/local/local.a'
1.402 s 0.26% action 'GoCompilePkg ddl/ingest/ingest.a'
8.886 s 1.62% action 'GoCompilePkg ddl/ddl.a'
3.788 s 0.69% action 'GoCompilePkg ddl/schematracker/schematracker.a'
7.091 s 1.29% action 'GoCompilePkg domain/domain.a'
2.962 s 0.54% action 'GoCompilePkg br/pkg/glue/glue.a'
64.251 s 11.71% action 'GoCompilePkg br/pkg/aws/aws.a'
6.616 s 1.21% action 'GoCompilePkg br/pkg/task/task.a'
3.315 s 0.60% action 'GoCompilePkg br/pkg/task/show/show.a'
28.612 s 5.21% action 'GoCompilePkg executor/executor.a'
24.501 s 4.47% action 'GoCompilePkg session/session.a'
9.404 s 1.71% action 'GoCompilePkg store/gcworker/gcworker.a'
7.626 s 1.39% action 'GoCompilePkg store/driver/driver.a'
8.102 s 1.48% action 'GoCompilePkg testkit/testkit.a'
3.498 s 0.64% action 'GoCompilePkg testkit/external/external.a'
25.698 s 4.68% action 'GoCompilePkg planner/core/casetest/casetest_test.internal.a'
2.696 s 0.49% action 'GoCompilePkg planner/core/casetest/casetest_test_test.external.a'
3.588 s 0.65% action 'GoCompilePkg planner/core/casetest/casetest_test~testmain.a'
77.429 s 14.11% action 'GoLink planner/core/casetest/casetest_test_/casetest_test'
0.29 ms 0.00% runfiles for //planner/core/casetest casetest_test
141.647 s 25.81% action 'Testing //planner/core/casetest casetest_test (shard 14 of 50)'
```

it will take 25% time for casetest to be completed.

so we need to speed up it.