basalt-26.3: kv/kvserver: TestStoreRangeMergeSplitRace_MergeWins failed

kv/kvserver.TestStoreRangeMergeSplitRace_MergeWins [failed](https://mesolite.cluster.engflow.com/invocations/default/bb5aa853-c1a6-446a-b698-5931847b6ea5?testReportRun=1&testReportShard=8&testReportAttempt=1#targets-Ly9wa2cva3Yva3ZzZXJ2ZXI6a3ZzZXJ2ZXJfdGVzdA==) on basalt-26.3 @ [9d68ab785115d04ed7ab69c88e35b730f63624e7](https://github.com/cockroachdb/cockroach/commits/9d68ab785115d04ed7ab69c88e35b730f63624e7):

```
=== RUN TestStoreRangeMergeSplitRace_MergeWins
test_log_scope.go:172: test logs captured to: outputs.zip/logTestStoreRangeMergeSplitRace_MergeWins1893374628
test_log_scope.go:82: use -show-logs to present logs inline
test_server_shim.go:146: using test tenant configuration from testserver factory defaults
client_merge_test.go:1655: merge failed: checking RHS manifest before merge: descriptor generation mismatch: expected 2, found 3
panic.go:694: -- test log scope end --
test logs left over in: outputs.zip/logTestStoreRangeMergeSplitRace_MergeWins1893374628
--- FAIL: TestStoreRangeMergeSplitRace_MergeWins (5.08s)
```

Parameters:
- attempt=1
- race=true
- run=1
- shard=8
Help

See also: [How To Investigate a Go Test Failure \(internal\)](https://cockroachlabs.atlassian.net/l/c/HgfXfJgM)

Same failure on other branches

- #174984 basalt-26.3.2-rc-20260908: kv/kvserver: TestStoreRangeMergeSplitRace_MergeWins failed [C-test-failure O-robot T-kv X-duplicate branch-basalt-26.3.2-rc-20260908 release-blocker]
- #174777 kv/kvserver: TestStoreRangeMergeSplitRace_MergeWins failed [C-test-failure O-robot T-kv branch-master release-blocker]

/cc @cockroachlabs/kv-triage

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Jira issue: CRDB-68189