[Infra] Remove SDK issue workaround

[martincostello]

Changes

Remove workaround for dotnet/sdk#51265 that should be fixed in the stable .NET 10 SDK that was missed from #6667.

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 86.72%. Comparing base (6648ff3) to head (cadc1ba).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6767      +/-   ##
==========================================
- Coverage   86.74%   86.72%   -0.02%     
==========================================
  Files         262      262              
  Lines       12319    12319              
==========================================
- Hits        10686    10684       -2     
- Misses       1633     1635       +2     

Flag	Coverage Δ
unittests-Project-Experimental	86.60% <ø> (+<0.01%)	⬆️
unittests-Project-Stable	86.57% <ø> (-0.13%)	⬇️
unittests-Solution	86.66% <ø> (-0.04%)	⬇️
unittests-UnstableCoreLibraries-Experimental	86.43% <ø> (ø)

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see 2 files with indirect coverage changes

[Copilot]

Pull request overview

This PR removes a workaround for a .NET SDK issue (dotnet/sdk#51265) that has been resolved in the stable .NET 10 SDK. The workaround was originally implemented to handle package pruning problems but is no longer necessary.

Key changes:

• Removed the RestoreEnablePackagePruning property workaround from the root build configuration
• Updated the Coyote test dependency approach to suppress security advisories instead of using direct package version overrides, avoiding NU1510 warnings in .NET 10 SDK

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Directory.Build.props	Removed the RestoreEnablePackagePruning workaround property that was addressing SDK issue #51265
test/Directory.Build.targets	Replaced System.Text.Json VersionOverride with NuGetAuditSuppress entries for security advisories to avoid .NET 10 SDK NU1510 warnings while still addressing the vulnerabilities

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