dev-cmd/generate-cask-ci-matrix: exclude ARM for AppImage casks

[biplavbarua]

This PR modifies the CI matrix generation to correctly handle AppImage casks, which typically do not support ARM architectures (e.g., Apple Silicon, Linux ARM).
Changes:

• Updates generate-cask-ci-matrix.rb to inspect Cask artifacts.
• If an AppImage artifact is detected, the test matrix is strictly limited to :intel (x86_64) runners.
• Adds a new test file dev-cmd/generate-cask-ci-matrix_spec.rb to verify this filtering logic.
  This unblocks CI for AppImage contributions by preventing them from being scheduled on incompatible runners.

[krehel]

Please follow the below instructions and report back results.

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) with your changes locally?

[biplavbarua]

Thanks for the guidance!

1. I have squashed the changes into a single clean commit.
2. I verified that brew tests --only=dev-cmd/generate-cask-ci-matrix passes locally.
3. I've confirmed that the logic now correctly attempts to simulate the Linux system to inspect on_linux blocks for architecture dependencies.
   If there is still a specific CI failure, could you point me to the log? My local checks are green.

[SMillerDev]

Could you add the matrix here that it generates for wizcli, Google chrome, a font and a cask that you edit to have the os architecture dependency case?