Add net6.0 to test targets

[Copilot]

Adds net6.0 as a test target alongside net10.0 (and net462 on Windows), and installs both SDKs on CI so the net6.0 test run has its runtime available. (net5.0 was skipped because Microsoft.NET.Test.Sdk 17.8.0's test host requires .NET 6+, causing zero tests to be discovered on net5.0.)

• PolyShim.Tests.csproj: TargetFrameworks → net6.0;net10.0 (net6.0 first)
• main.yml: passes dotnet-version to the reusable workflow to install both 6.0.x and 10.0.x; global.json stays pinned to 10.0.100 as the build SDK

[Copilot]

Pull request overview

Adds .NET 5 (net5.0) as an additional test target so the test suite runs on both net5.0 and net10.0 (plus net462 on Windows), and updates CI to install the required .NET SDKs.

Changes:

• Multi-target PolyShim.Tests for net5.0 and net10.0 (with net462 appended on Windows).
• Update the GitHub Actions workflow to install both 5.0.x and 10.0.x SDKs for CI runs.

Reviewed changes

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

File	Description
PolyShim.Tests/PolyShim.Tests.csproj	Adds net5.0 to TargetFrameworks to run tests against .NET 5 and .NET 10.
.github/workflows/main.yml	Passes a multi-version dotnet-version input so CI installs SDKs for both net5.0 and net10.0 test runs.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.88%. Comparing base (9387540) to head (c243ab8).
⚠️ Report is 1 commits behind head on prime.

Additional details and impacted files

@@            Coverage Diff             @@
##            prime     #112      +/-   ##
==========================================
+ Coverage   90.03%   90.88%   +0.85%     
==========================================
  Files         269      269              
  Lines        4604     4607       +3     
  Branches      367      378      +11     
==========================================
+ Hits         4145     4187      +42     
+ Misses        378      337      -41     
- Partials       81       83       +2     

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[Tyrrrz]

@copilot why are we getting 0 tests ran for .NET 5?

[Copilot]

@copilot why are we getting 0 tests ran for .NET 5?

The test host bundled with Microsoft.NET.Test.Sdk 17.8.0 requires .NET 6+ to run. Since .NET 5 went end-of-life in May 2022, vstest's in-process test host can't initialize against the net5.0 DLL, which is why it silently reports "No test is available" instead of a proper error.

If testing an older .NET version is the goal, net6.0 (LTS until Nov 2024) or net8.0 (current LTS) would work with the current package versions. Should I swap net5.0 for one of those?

[Tyrrrz]

@copilot let's try net6.0. Unfortunately, net8.0 is too new for our purposes.

[Copilot]

@copilot let's try net6.0. Unfortunately, net8.0 is too new for our purposes.

Done in c243ab8. Swapped net5.0 → net6.0 in the test project and 5.0.x → 6.0.x in the CI workflow.