[Repo] Attempting to stabilize the API Compatibility CI job

[CodeBlanch]

Switches the powershell script to run once per project instead of in parallel for each target framework in a project.

This should resolve these annoying CI failures:

  Working directory for previous package versions not found, creating...
  Working directory for previous package versions not found, creating...
  Retrieving OpenTelemetry @1.3.1 for compatibility check
  Retrieving OpenTelemetry @1.3.1 for compatibility check
  Invoke-WebRequest : The process cannot access the file 
  'D:\a\opentelemetry-dotnet\opentelemetry-dotnet\src\LastMajorVersionBinaries\OpenTelemetry.1.3.1.zip' because it is 
  being used by another process.

[codecov]

Codecov Report

Merging #3766 (e273657) into main (7852797) will decrease coverage by 0.21%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3766      +/-   ##
==========================================
- Coverage   87.38%   87.16%   -0.22%     
==========================================
  Files         277      277              
  Lines       10068    10068              
==========================================
- Hits         8798     8776      -22     
- Misses       1270     1292      +22     

Impacted Files	Coverage Δ
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	35.71% <0.00%> (-42.86%)	⬇️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	36.36% <0.00%> (-40.91%)	⬇️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	73.52% <0.00%> (-5.89%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	91.75% <0.00%> (-3.30%)	⬇️
...ZPages/Implementation/ZPagesExporterEventSource.cs	62.50% <0.00%> (+6.25%)	⬆️