Request: open PR from tested fork branch

I have a tested fix branch for the reference test suite, but this repository currently restricts opening pull requests to collaborators only, so GitHub blocks PR creation from my fork.

Compare link:
https://github.com/google/mantis/compare/main...Dphoshoba:mantis:test/fail-soft-reference-deps

Summary:
- Make `reference/test_suite.py` fail-soft when optional Google ADK dependencies are unavailable.
- Add a minimal dependency-gate test so lightweight pytest environments still return success instead of collection failure.

Verification run locally:
- `python -m pytest -q` → `1 passed, 1 skipped in 0.08s`
- `python -m pre_commit run --all-files` → passed

Branch:
https://github.com/Dphoshoba/mantis/tree/test/fail-soft-reference-deps

Could a collaborator either open this compare as a PR or enable PR creation for this repository?

Start with the linked compare and branch, especially reference/test_suite.py, and reproduce the reported result with python -m pytest -q and python -m pre_commit run --all-files. The requested work is already implemented; done means a collaborator opens the compare as a pull request or enables fork-based PR creation.

Written by the indexing model from the issue text.