[CHORE] Remove usage of credentials in workflows

[jaychia]

This allows PRs from forks to be green

• Tests which require credentials are now only run on main, on a separate job called integration-test-io-credentialed
• The fixtures providing IOConfigs now conditionally set anonymous=True depending on whether the test is triggered with the --credentials option, which is a custom option added to pytest

[codecov]

Codecov Report

Merging #1686 (de005eb) into main (cb1fb22) will increase coverage by 0.06%.
Report is 3 commits behind head on main.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1686      +/-   ##
==========================================
+ Coverage   85.04%   85.10%   +0.06%     
==========================================
  Files          55       55              
  Lines        5341     5345       +4     
==========================================
+ Hits         4542     4549       +7     
+ Misses        799      796       -3     

see 1 file with indirect coverage changes

[samster25]

Looks great!