db-console,jobs: retrieving nonexistent job 500s

Attempting to retrieve a nonexistent job 500s, presenting an error to the user that suggests a more serious problem:

```
E230322 14:36:21.303601 1315371654 server/admin.go:2447 ⋮ [T1,n1] 31 could not get job for job_id 845382943526912007; 0 rows returned
(1) attached stack trace
-- stack trace:
| github.com/cockroachdb/cockroach/pkg/server.jobHelper
| github.com/cockroachdb/cockroach/pkg/server/admin.go:2480
| github.com/cockroachdb/cockroach/pkg/server.(*adminServer).Job
| github.com/cockroachdb/cockroach/pkg/server/admin.go:2445
| github.com/cockroachdb/cockroach/pkg/server/serverpb._Admin_Job_Handler.func1
| github.com/cockroachdb/cockroach/pkg/server/serverpb/bazel-out/k8-opt/bin/pkg/server/serverpb/serverpb_go_proto_/github.com/cockroachdb/cockroach/pkg/server/serverpb/admin.pb.go:6192
| github.com/cockroachdb/cockroach/pkg/util/tracing/grpcinterceptor.ServerInterceptor.func1
| github.com/cockroachdb/cockroach/pkg/util/tracing/grpcinterceptor/grpc_interceptor.go:115
| google.golang.org/grpc.chainUnaryInterceptors.func1.1
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:1162
| github.com/cockroachdb/cockroach/pkg/rpc.NewServerEx.func3
| github.com/cockroachdb/cockroach/pkg/rpc/pkg/rpc/context.go:276
| google.golang.org/grpc.chainUnaryInterceptors.func1.1
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:1165
| github.com/cockroachdb/cockroach/pkg/rpc.NewServerEx.func1.1
| github.com/cockroachdb/cockroach/pkg/rpc/pkg/rpc/context.go:243
| github.com/cockroachdb/cockroach/pkg/util/stop.(*Stopper).RunTaskWithErr
| github.com/cockroachdb/cockroach/pkg/util/stop/stopper.go:322
| github.com/cockroachdb/cockroach/pkg/rpc.NewServerEx.func1
| github.com/cockroachdb/cockroach/pkg/rpc/pkg/rpc/context.go:241
| google.golang.org/grpc.chainUnaryInterceptors.func1.1
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:1165
| google.golang.org/grpc.chainUnaryInterceptors.func1
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:1167
| github.com/cockroachdb/cockroach/pkg/server/serverpb._Admin_Job_Handler
| github.com/cockroachdb/cockroach/pkg/server/serverpb/bazel-out/k8-opt/bin/pkg/server/serverpb/serverpb_go_proto_/github.com/cockroachdb/cockroach/pkg/server/serverpb/admin.pb.go:6194
| google.golang.org/grpc.(*Server).processUnaryRPC
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:1340
| google.golang.org/grpc.(*Server).handleStream
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:1713
| google.golang.org/grpc.(*Server).serveStreams.func1.2
| google.golang.org/grpc/external/org_golang_google_grpc/server.go:965
| runtime.goexit
| GOROOT/src/runtime/asm_amd64.s:1594
Wraps: (2) could not get job for job_id 845382943526912007; 0 rows returned
```

Jira issue: CRDB-25774