* ZJIT: Add test exclusions for ZJIT
* ZJIT: Update test targets and documentation
- Rename `zjit-test-all` to `zjit-check`
- Add `zjit-test-all` target to zjit.mk to run all Ruby tests with ZJIT enabled
excluding known failing tests
- Update documentation and CI workflow to reflect the new targets
* Add a make target to run all ZJIT tests
* Remove an unused variable
* Write up a document about testing
* Explain zjit-test-all first
* Clarify what's zjit-test-all