Temporarily exclude PDF if D10

[rosiel]

What does this Pull Request do?

Drupal 10 tests for all our modules fail because Islandora CI installs PDF, which doesn't have a D10 version yet.

It would be really useful to be able to test the majority of our modules, which do not require pdf, on Drupal 10. Therefore I'm proposing this as a temporary fix.

• Related GitHub Issue: (link)

• Other Relevant Links:
  Example PR: Drupal 10 readiness jsonld#69

What's new?

Skip PDF installation if Drupal 10.

How should this be tested?

I'm not sure, but once committed, D10 pull requests should be tested with a suite that doesn't fail when trying to install the pdf module.

Documentation Status

• Does this change existing behaviour that's currently documented? NO
• Does this change require new pages or sections of documentation? NO
• Who does this need to be documented for? NO
• Associated documentation pull request(s): ___ or documentation issue ___ N/A

Additional Notes:

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

Interested parties

@adam-vessey @whikloj