Fix compatibility with Matplotlib 3.5 and astropy 5.0

[astrofrog]

No description provided.

[codecov]

Codecov Report

Merging #2250 (ea0dfd2) into main (4b5c79d) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2250      +/-   ##
==========================================
+ Coverage   88.04%   88.05%   +0.01%     
==========================================
  Files         247      247              
  Lines       23172    23169       -3     
==========================================
  Hits        20402    20402              
+ Misses       2770     2767       -3     

Impacted Files	Coverage Δ
glue/viewers/image/frb_artist.py	97.56% <100.00%> (-0.17%)	⬇️
glue/viewers/matplotlib/qt/widget.py	77.27% <0.00%> (+3.40%)	⬆️

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