What is the change? Why is it being made?

This PR improves the ARMI docs in a few different ways:

• I believe the SCR was not building correctly on ARMI main, because the PR_NUMBER env variable was being set incorrectly in the doc.yaml file. This is why I had to pull PDFs from the PRs for this past ARMI release.
• There was a gallery example that broke when we made the FAIL_ON_RANGE=True change.
• Also, I refactored the automateSCR.py script to make it easier to run locally (I just made one of the arguments optional).

closes #2397

SCR Information

Change Type: docs

One-Sentence Rationale: The SCR should, ideally, build from PRs and from the main branch.

One-line Impact on Requirements: NA

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.
• The documentation is still up-to-date in the doc folder.
• The code style follows good practices.
• The dependencies are still up-to-date in pyproject.toml.