Fix miscellaneous small holiday errors

[gaibo]

Modified an incorrect comment on US Memorial Day and corrected some holiday names.
Nothing affects the code, only trying to contribute because I noticed some issues while reading through.

[codecov]

Codecov Report

Merging #26912 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26912      +/-   ##
==========================================
- Coverage   91.87%   91.86%   -0.01%     
==========================================
  Files         180      180              
  Lines       50712    50712              
==========================================
- Hits        46590    46586       -4     
- Misses       4122     4126       +4

Flag	Coverage Δ
#multiple	90.45% <100%> (ø)	⬆️
#single	41.09% <100%> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/holiday.py	93.1% <100%> (ø)	⬆️
pandas/io/gbq.py	88.88% <0%> (-11.12%)	⬇️
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 baa77c3...c59f28c. Read the comment docs.

[codecov]

Codecov Report

Merging #26912 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #26912      +/-   ##
==========================================
- Coverage   91.87%   91.86%   -0.01%     
==========================================
  Files         180      180              
  Lines       50712    50712              
==========================================
- Hits        46590    46586       -4     
- Misses       4122     4126       +4

Flag	Coverage Δ
#multiple	90.45% <100%> (ø)	⬆️
#single	41.09% <100%> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/tseries/holiday.py	93.1% <100%> (ø)	⬆️
pandas/io/gbq.py	88.88% <0%> (-11.12%)	⬇️
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 baa77c3...c59f28c. Read the comment docs.

[jreback]

thanks @gaibo