Skip csharp integration tests on macos-26

[oscarsj]

C# integration tests for standalone dependencies are failing on macOS 26 runners due to Mono/NuGet compatibility issues. These tests already skip on macOS 15 for the same reason - unexpected .NET Framework reference assemblies appear in the missingpackages directory, causing test output mismatches.

Changes

Extended the existing platform skip conditions to include macOS 26:

# Before
@pytest.mark.only_if(
    runs_on.linux
    or (runs_on.macos and runs_on.x86_64 and not runs_on.macos_15)
)

# After
@pytest.mark.only_if(
    runs_on.linux
    or (runs_on.macos and runs_on.x86_64 and not runs_on.macos_15 and not runs_on.macos_26)
)

Updated 4 test files:

• standalone_dependencies_no_framework/test.py
• standalone_dependencies_nuget/test.py
• standalone_dependencies_nuget_no_sources/test.py
• standalone_dependencies_nuget with_space/test.py

Tests continue to run on Linux and macOS x86_64 (excluding versions 15 and 26).

[Copilot]

Pull request overview

Extends existing platform-based skips so C# standalone-dependency integration tests are not run on macOS 26 runners where Mono/NuGet behavior causes output mismatches.

Changes:

• Updated @pytest.mark.only_if(...) predicates to additionally exclude runs_on.macos_26.
• Adjusted test-file comments to mention macos-26.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
csharp/ql/integration-tests/posix/standalone_dependencies_nuget_no_sources/test.py	Excludes macOS 26 from the only_if predicate and updates skip comment.
csharp/ql/integration-tests/posix/standalone_dependencies_nuget/test.py	Excludes macOS 26 from the only_if predicate and updates skip comment.
csharp/ql/integration-tests/posix/standalone_dependencies_nuget with_space/test.py	Excludes macOS 26 from the only_if predicate and updates skip comment.
csharp/ql/integration-tests/posix/standalone_dependencies_no_framework/test.py	Excludes macOS 26 from the only_if predicate and updates skip comment.

[Copilot]

This skip predicate (and its accompanying comment) is duplicated across multiple test files in this PR. To reduce duplication and keep the excluded macOS version list consistent, consider centralizing the predicate in a shared helper (e.g., a variable/fixture in conftest.py or a small utility function) and reusing it across these tests.

See below for a potential fix:

def _supports_mono_nuget():
    return (
        runs_on.linux
        or (
            runs_on.macos
            and runs_on.x86_64
            and not runs_on.macos_15
            and not runs_on.macos_26
        )
    )


@pytest.mark.only_if(_supports_mono_nuget())

[oscarsj]

@copilot can you implement this suggestion?

[Copilot]

@oscarsj I've opened a new pull request, #21340, to work on those changes. Once the pull request is ready, I'll request review from you.

[michaelnebel]

LGTM!