CI: Prevent cron job workflow runs on forks

[nkphysics]

This PR implements conditions to CI actions to prevent scheduled cron job actions from running on forks to resolve #3457

Changes

• Added explicit fork-protection to all scheduled CI workflows using the pattern already in use across the open source python ecosystem:

  if: github.repository == 'astropy/astroquery' || github.event_name != 'schedule'
  

This allows normal push, pull_request, tag, and manual triggers to continue working on forks (still useful for testing PRs), while completely skipping scheduled runs on any fork. I also left a comment in the workflows for anyone that wants to enable the workflows on their forks.

I applied this to the following workflows:

• .github/workflows/ci_crontests.yml

• .github/workflows/ci_devtest.yml

• .github/workflows/ci_tests.yml (both the tests and egg_info jobs)

• .github/workflows/ci-online-crontests.yml left it alone as it already uses github.repository == 'astropy/astroquery' condition.

Also, I know that this was not covered in the issue ticket, but I also applied a condition to the codeql workflow since I looked at my fork and it was running on a schedule there too.

I restricted to the upstream repository only using the stricter condition if: github.repository == 'astropy/astroquery' since the results from forks are ignored by GitHub anyway, so its kinda just a waste.

I'm not sure if this requires a changelog entry. I tried looking at some closed infra/CI PRs and many were marked with a "no-changelog-needed" tag, so I won't include one for now, but can add one if its needed.

Also can make similar changes to astropy/pyvo#705 if that would be helpful @bsipocz.

Hope this is a helpful ! 😄

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.48%. Comparing base (3418e41) to head (0723c36).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3468   +/-   ##
=======================================
  Coverage   71.48%   71.48%           
=======================================
  Files         234      234           
  Lines       20096    20096           
=======================================
  Hits        14365    14365           
  Misses       5731     5731           

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