Disable CI builds that fail systematically

[astrofrog]

Some of the CI builds always fail, and make it hard to see if a given PR is otherwise passing, so I am disabling those builds for now.

[codecov]

Codecov Report

Merging #2268 (996d593) into main (b13535d) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2268   +/-   ##
=======================================
  Coverage   88.03%   88.04%           
=======================================
  Files         247      247           
  Lines       23180    23196   +16     
=======================================
+ Hits        20407    20422   +15     
- Misses       2773     2774    +1     

Impacted Files	Coverage Δ
glue/conftest.py	53.03% <0.00%> (-1.52%)	⬇️
glue/default_config.py	0.00% <0.00%> (ø)
glue/config.py	85.07% <0.00%> (+0.03%)	⬆️
glue/core/command.py	93.85% <0.00%> (+0.03%)	⬆️
glue/core/simpleforms.py	98.00% <0.00%> (+0.08%)	⬆️
glue/viewers/custom/qt/custom_viewer.py	93.45% <0.00%> (+0.14%)	⬆️
glue/core/fitters.py	91.77% <0.00%> (+0.92%)	⬆️

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