[repo/Quartz] Prepare to .NET9

[Kielek]

Changes

Follow up #2251

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• [ ] Unit tests added/updated
• [ ] Appropriate CHANGELOG.md files updated for non-trivial changes
• [ ] Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.76%. Comparing base (71655ce) to head (8062906).
Report is 579 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2293      +/-   ##
==========================================
+ Coverage   73.91%   78.76%   +4.84%     
==========================================
  Files         267        5     -262     
  Lines        9615      113    -9502     
==========================================
- Hits         7107       89    -7018     
+ Misses       2508       24    -2484     

Flag	Coverage Δ
unittests-Instrumentation.Quartz	78.76% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
....Quartz/Implementation/QuartzDiagnosticListener.cs	82.60% <100.00%> (-4.49%)	⬇️

... and 263 files with indirect coverage changes

[CodeBlanch]

LGTM