Stabilize parallel batch snapshot refresh timeout in the net9 full suite

[Widthdom]

Discovered while validating #4909. The net9.0 full suite failed twice at CodeIndex.Tests.QueryCommandRunnerTests.RunBatch_ParallelRefreshesDetachedSnapshotsBetweenItems_Issue4872 because its 75-second wait timed out. The same test passed when run alone in 74 seconds. Command: dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release -f net9.0 --no-build --no-restore --settings tests/CodeIndex.Tests/CodeIndex.Tests.runsettings --blame-crash --blame-hang --blame-hang-timeout 5m. Expected: the test should have sufficient deterministic headroom in the full compatibility suite without weakening its concurrency assertions.

[Widthdom]

I have started working on this issue on branch fix-issue5015.