[Benchmark X64] [Copilot] Port alternation switch optimization from source g ...

[MihuBot]

Job completed in 15 minutes 41 seconds (remote runner delay: 1 minute 11 seconds).
dotnet/runtime#122959
Using arguments: benchmark Regex
Main commit: dotnet/runtime@b19edc0
PR commit: dotnet/runtime@03e7c36

ERROR: System.Exception: /usr/lib/dotnet/dotnet run -c Release --framework net10.0 -- --filter *Regex* -h Job StdDev RatioSD Median Min Max OutlierMode MemoryRandomization Gen0 Gen1 Gen2 --corerun /ramdisk/artifacts-main/corerun /ramdisk/artifacts-pr/corerun  failed with exit code 1
   at Runner.JobBase.RunProcessAsync(String fileName, String arguments, List`1 output, String logPrefix, String workDir, Boolean checkExitCode, Func`2 processLogs, Boolean suppressOutputLogs, Boolean suppressStartingLog, ProcessPriorityClass priority, List`1 envVars, CancellationToken cancellationToken) in /home/runtime-utils/Runner/JobBase.cs:line 472
   at Runner.Jobs.BenchmarkLibrariesJob.RunBenchmarksAsync(String[] coreRunPaths) in /home/runtime-utils/Runner/Jobs/BenchmarkLibrariesJob.cs:line 247
   at Runner.Jobs.BenchmarkLibrariesJob.RunJobCoreAsync() in /home/runtime-utils/Runner/Jobs/BenchmarkLibrariesJob.cs:line 82
   at Runner.JobBase.RunJobAsync() in /home/runtime-utils/Runner/JobBase.cs:line 164

[MihuBot]

@stephentoub

[MihaZupan]

[00:15:41] /ramdisk/performance/src/benchmarks/micro/MicroBenchmarks.csproj : error NU1605: Warning As Error: Detected package downgrade: System.Collections.Immutable from 9.0.0 to 8.0.0. Reference the package directly from the project to select a different version. 
[00:15:41] /ramdisk/performance/src/benchmarks/micro/MicroBenchmarks.csproj : error NU1605:  MicroBenchmarks -> BenchmarkDotNet.Extensions -> BenchmarkDotNet 0.16.0-custom.20260120.101 -> Microsoft.CodeAnalysis.CSharp 5.0.0 -> System.Collections.Immutable (>= 9.0.0) 
[00:15:41] /ramdisk/performance/src/benchmarks/micro/MicroBenchmarks.csproj : error NU1605:  MicroBenchmarks -> System.Collections.Immutable (>= 8.0.0-0)

Lemme see what's going on there...