[release] Core stable release 1.15.2 updates

[otelbot-dotnet]

Note: This PR was opened automatically by the post-release workflow.

Merge once packages are available on NuGet and the build passes.

Changes

• Sets OTelLatestStableVer in Directory.Packages.props to 1.15.2.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.32%. Comparing base (1a1be0e) to head (97accc6).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7049   +/-   ##
=======================================
  Coverage   88.32%   88.32%           
=======================================
  Files         270      270           
  Lines       12758    12758           
=======================================
  Hits        11269    11269           
  Misses       1489     1489           

Flag	Coverage Δ
unittests-Project-Experimental	88.02% <ø> (-0.17%)	⬇️
unittests-Project-Stable	88.27% <ø> (+0.13%)	⬆️
unittests-Solution	87.98% <ø> (-0.28%)	⬇️
unittests-UnstableCoreLibraries-Experimental	41.39% <ø> (ø)

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