Skip tests using nuget from signed builds

[T-Gro]

(network isolation need for signed builds)

[github-actions]

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cc @dotnet/fsharp-team-msft

[Copilot]

Pull request overview

This PR introduces new test attributes to skip tests that require NuGet package restore when running in signed builds. Signed builds operate under network isolation for security reasons, which prevents NuGet package restoration from working. The PR adds three new xUnit test attributes (FactSkipOnSignedBuild, TheorySkipOnSignedBuild, and FactForNETCOREAPPSkipOnSignedBuild) that check the SIGNTYPE environment variable and skip tests when it equals "Real". These attributes are then applied to approximately 30 tests across the test suite that use #r "nuget:" directives or NuGet packages.

Key changes:

• Added SignedBuildSkip module with reusable skip logic in test utilities
• Created three new conditional skip attributes for different test scenarios
• Applied skip attributes to FSI printing tests, regression tests, and scripting/dependency manager tests

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/FSharp.Test.Utilities/Utilities.fs	Defines SignedBuildSkip module and three new test attributes (FactSkipOnSignedBuild, TheorySkipOnSignedBuild, FactForNETCOREAPPSkipOnSignedBuild) that check for signed builds via the SIGNTYPE environment variable
tests/fsharp/tests.fs	Applies FactSkipOnSignedBuild attribute to FSI printing tests (which use NuGet via test.fsx) and large input regression tests (12322, 13219, 13710) that require NuGet packages
tests/FSharp.Compiler.Service.Tests/ProjectAnalysisTests.fs	Marks one test that uses #r nuget directives with the skip attribute
tests/FSharp.Compiler.Private.Scripting.UnitTests/FSharpScriptTests.fs	Applies skip attributes to multiple scripting tests that use NuGet packages, including ML.NET, FSharpPlus, and other NuGet-dependent scenarios
tests/FSharp.Compiler.Private.Scripting.UnitTests/DependencyManagerInteractiveTests.fs	Marks dependency manager tests that restore and use NuGet packages with the skip attribute