Workaround for matplotlib rc_context issue

[mwaskom]

It's not necessary to use rc_context because we know exactly what parameter we want to change (although it does require implementing a custom context manager).

The only effect of this rcparam is to toggle the layout parameter of plt.figure() (actually mpl.figure.Figure), so really we could just pass a parameter there. But matplotlib is in the middle of a dance with the tight_layout/layout parameters, so handling the various forwards/backwards compatibility issues seems too complicated for now.

Fixes #2914
More context at matplotlib/matplotlib#23298

[codecov]

Codecov Report

Merging #2925 (3132feb) into master (f581300) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2925   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files          69       69           
  Lines       22866    22874    +8     
=======================================
+ Hits        22464    22472    +8     
  Misses        402      402           

Impacted Files	Coverage Δ
seaborn/axisgrid.py	97.17% <100.00%> (ø)
seaborn/utils.py	95.08% <100.00%> (+0.11%)	⬆️