[CI] Test with php 8.1.

[rosiel]

GitHub Issue: none (CI)

Tests are sneakily failing (they're green but are actually broken, failing on Drupal 10.). Recent Example.

What does this Pull Request do?

Updates the test matrix by

• removing php 7.3
• adding php 8.0, 8.1
• including drupal pre-release 9.5.x-dev
• removing drupal 10 till we can expect it to pass. (at least make it installable on D10!) Failing while showing the test as green gives a false expectation that it works on Drupal 10.
• making all tests mandatory

Since we're no longer testing on it, officially deprecate Drupal 8.

How should this be tested?

• Do tests pass?

Additional Notes:

Any additional information that you think would be helpful when reviewing this
PR.

Interested parties

@Islandora/committers