Fix IL3050 test build warnings

[Widthdom]

Summary

• Rebased the PR scope onto the latest origin/main, which now contains the dotnet test fails with Native AOT IL3050 analyzer errors #2786 implementation commits.
• Keep this PR focused on the bilingual fixed changelog fragment for dotnet test fails with Native AOT IL3050 analyzer errors #2786.

Validation

• dotnet format CodeIndex.sln --verify-no-changes --no-restore --verbosity minimal
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter FullyQualifiedName~McpServerTests -p:UseSharedCompilation=false
• dotnet build CodeIndex.sln -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check
• Adversarial review: No blocking/actionable issues found.

Documentation and Changelog

• Added changelog.d/unreleased/2786.fixed.md.
• No documentation update was required in this PR because the code-side dotnet test fails with Native AOT IL3050 analyzer errors #2786 CI/test-build behavior is already present on latest origin/main.

Follow-up Candidates

• None.

Fixes #2786