TST: Fix mpl 3.0.3 grid settings test failure

[simonjayhawkins]

• closes test failures locally with matplotlib: 3.0.3 #26734
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[jreback]

sure merge on green.

[codecov]

Codecov Report

Merging #26737 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26737      +/-   ##
==========================================
- Coverage   91.78%   91.77%   -0.01%     
==========================================
  Files         174      174              
  Lines       50703    50703              
==========================================
- Hits        46538    46534       -4     
- Misses       4165     4169       +4

Flag	Coverage Δ
#multiple	90.37% <ø> (ø)	⬆️
#single	41.81% <ø> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

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[codecov]

Codecov Report

Merging #26737 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26737      +/-   ##
==========================================
- Coverage   91.78%   91.77%   -0.01%     
==========================================
  Files         174      174              
  Lines       50703    50703              
==========================================
- Hits        46538    46534       -4     
- Misses       4165     4169       +4

Flag	Coverage Δ
#multiple	90.37% <ø> (ø)	⬆️
#single	41.81% <ø> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cf25c5c...dd68411. Read the comment docs.