Poison baseline should ignore package version diffs

[ellahathaway]

The poison report currently includes package-specific versions in artifact paths. When a package version changes (e.g., after a rebootstrap), the baseline comparison in the poison diff test can fail—even if the actual leaks have not changed. This results in false positives: the test fails when comparing the poison baselines simply because the package version is different, not because new leaks have occurred.

See these package versions as examples: https://github.com/dotnet/dotnet/blob/d6793e0c28de49443b86ff0c82c269c84054757f/test/Microsoft.DotNet.SourceBuild.Tests/assets/PoisonTests/PoisonUsage.txt#L14-L18

Poison detection should not fail when package versions are updated. The comparison should ignore version changes for packages. We should update the poison report logic and baseline comparison to disregard package version changes, so only real leak changes cause test failures.