infra: update dependabot.yml to ignore specific dependencies

[rmshaffer]

Issue #, if available:

Description of changes:

Testing done:

Merge Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your pull request.

General

• I have read the CONTRIBUTING doc
• I have read docs/INSTRUCTIONS.md and if necessary, added to docs/ENTRIES.json and run docs/build_readme.sh

Tests

• I have verified my changes pass pytest test/ (see TESTING.md)
• If adding to EXCLUDED_NOTEBOOKS, I have included reason in the comment (e.g. # Reason: requires GPU runtime)
• If modifying a notebook, I have verified no broken outputs or missing imports

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.