Reducing warnings while building the docs

[john-science]

What is the change?

The goal of this PR is actually two-fold:

1. Un-break the doc build.
   • A recent PR broke the doc build, because running the docs means running a test reactor, which moved.
2. Get rid of 1,000 warnings when we build the docs.
   • We have impl and test tags for Sphinx Needs requirements in ARMI, but the requirements aren't in ARMI, so this raises many warnings when building the docs. I just suppress those.

Why is the change being made?

You can see proof that this doc build ran and worked correctly here.

close #1876

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes have been updated if necessary.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in pyproject.toml.