fix: AOT tests silently skip on local machines

[thomhurst]

Description

File: TUnit.Engine.Tests/InvokableTestBase.cs (Lines 82-85)

if (Environment.GetEnvironmentVariable("GITHUB_ACTIONS") != "true")
{
    return;  // Silently skips!
}

AOT tests silently return without any indication when not running in GitHub Actions. Developers might think they've tested everything when they haven't.

Suggested Fix

• Use [Skip("AOT testing only available in CI")] or equivalent instead of silent return
• Log a warning when AOT mode is skipped
• Document in CLAUDE.md how to manually run AOT tests locally
• Add a marker in test output showing which modes actually executed