BDN: Failed to build in Parallel, switching to sequential build

I fairly frequently see the message "Failed to build in Parallel, switching to sequential build":
```
C:\gh\performance\src\benchmarks\micro>dotnet run -c Release -f net6.0 -- --filter *BenchI.Array2* *Bytemark.BenchLUDecomp* --coreRun C:\gh\runtime2\artifacts\tests\coreclr\windows.x64.Release\Tests\Core_Root\CoreRun.exe C:\gh\runtime\artifacts\tests\coreclr\windows.x64.Release\Tests\Core_Root\CoreRun.exe -e GitHub
// Validating benchmarks:
// ***** BenchmarkRunner: Start *****
// ***** Found 4 benchmark(s) in total *****
// ***** Building 2 exe(s) in Parallel: Start *****
// ***** Done, took 00:00:39 (39.27 sec) *****
// ***** Failed to build in Parallel, switching to sequential build *****
// ***** Done, took 00:00:59 (59.6 sec) *****
```

It seems surprising this first part of the process takes so much time, but it seems like whatever it's trying to do in parallel isn't working, and ends up wasting a bunch of time.