[repo/shared] 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

Attention: Patch coverage is 39.28571% with 17 lines in your changes missing coverage. Please review.

Project coverage is 72.81%. Comparing base (71655ce) to head (b3355d1).
Report is 557 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Shared/GrpcTagHelper.cs	11.11%	16 Missing ⚠️
src/Shared/NullableAttributes.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2267      +/-   ##
==========================================
- Coverage   73.91%   72.81%   -1.10%     
==========================================
  Files         267      359      +92     
  Lines        9615    13778    +4163     
==========================================
+ Hits         7107    10033    +2926     
- Misses       2508     3745    +1237     

Flag	Coverage Δ
unittests-Contrib.Shared.Tests	77.13% <39.28%> (?)
unittests-Exporter.Geneva	62.34% <ø> (?)
unittests-Exporter.InfluxDB	95.14% <ø> (?)
unittests-Exporter.Instana	71.24% <ø> (?)
unittests-Exporter.OneCollector	94.34% <ø> (?)
unittests-Exporter.Stackdriver	75.73% <ø> (?)
unittests-Extensions	88.63% <ø> (?)
unittests-Extensions.Enrichment	100.00% <ø> (?)
unittests-Instrumentation.AWS	86.09% <ø> (?)
unittests-Instrumentation.AspNet	76.73% <ø> (?)
unittests-Instrumentation.AspNetCore	70.06% <ø> (?)
unittests-Instrumentation.ConfluentKafka	14.12% <ø> (?)
unittests-Instrumentation.ElasticsearchClient	79.87% <ø> (?)
unittests-Instrumentation.EntityFrameworkCore	57.06% <ø> (?)
unittests-Instrumentation.EventCounters	76.36% <ø> (?)
unittests-Instrumentation.GrpcNetClient	79.61% <ø> (?)
unittests-Instrumentation.Hangfire	93.58% <ø> (?)
unittests-Instrumentation.Http	73.57% <ø> (?)
unittests-Instrumentation.Owin	85.97% <ø> (?)
unittests-Instrumentation.Process	100.00% <ø> (?)
unittests-Instrumentation.Quartz	78.94% <ø> (?)
unittests-Instrumentation.Runtime	97.53% <ø> (?)
unittests-Instrumentation.SqlClient	91.36% <ø> (?)
unittests-Instrumentation.StackExchangeRedis	71.21% <ø> (?)
unittests-Instrumentation.Wcf	78.34% <ø> (?)
unittests-PersistentStorage	65.78% <ø> (?)
unittests-Resources.AWS	79.16% <ø> (?)
unittests-Resources.Azure	84.56% <ø> (?)
unittests-Resources.Container	67.34% <ø> (?)
unittests-Resources.Gcp	71.15% <ø> (?)
unittests-Resources.Host	73.91% <ø> (?)
unittests-Resources.OperatingSystem	76.98% <ø> (?)
unittests-Resources.Process	100.00% <ø> (?)
unittests-Resources.ProcessRuntime	78.26% <ø> (?)
unittests-Sampler.AWS	87.74% <ø> (?)

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

Files with missing lines	Coverage Δ
src/Shared/ActivityInstrumentationHelper.cs	100.00% <100.00%> (ø)
src/Shared/DatabaseSemanticConventionHelper.cs	83.33% <100.00%> (ø)
src/Shared/PropertyFetcher.AOT.cs	97.82% <100.00%> (ø)
src/Shared/RequestDataHelper.cs	81.25% <100.00%> (ø)
src/Shared/NullableAttributes.cs	0.00% <0.00%> (ø)
src/Shared/GrpcTagHelper.cs	54.05% <11.11%> (ø)

... and 372 files with indirect coverage changes

[CodeBlanch]

LGTM