[repo] Fix a couple issues in automation workflows/scripts

[CodeBlanch]

Changes

• Don't require OPENTELEMETRYBOT_GITHUB_TOKEN secret in automation.yml. It is designed to work without it but because it is required all workflows which use automation blow up when run on forks if they don't have the secret defined.

• Use proper PowerShell envvar syntax in post-release.psm1.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.05%. Comparing base (6250307) to head (e9542b0).
Report is 253 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5680      +/-   ##
==========================================
+ Coverage   83.38%   86.05%   +2.67%     
==========================================
  Files         297      254      -43     
  Lines       12531    11054    -1477     
==========================================
- Hits        10449     9513     -936     
+ Misses       2082     1541     -541     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	85.98% <ø> (?)
unittests-Project-Stable	85.98% <ø> (?)
unittests-Solution	86.03% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	20.12% <ø> (?)

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see 126 files with indirect coverage changes