TST: Remove clipboard-excel test warnings

[gfyoung]

Closes #19010.

[codecov]

Codecov Report

Merging #19052 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #19052      +/-   ##
==========================================
- Coverage   91.57%   91.54%   -0.03%     
==========================================
  Files         150      150              
  Lines       48942    48942              
==========================================
- Hits        44818    44806      -12     
- Misses       4124     4136      +12

Flag	Coverage Δ
#multiple	89.91% <ø> (-0.03%)	⬇️
#single	41.75% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/plotting/_converter.py	65.22% <0%> (-1.74%)	⬇️

---

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 ab000a9...c31697e. Read the comment docs.

[jreback]

thanks @gfyoung