DOC: Small whatsnew cleanups

[jschendel]

Some small fixes I noticed reading over the whatsnew

[codecov]

Codecov Report

Merging #26643 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26643      +/-   ##
==========================================
- Coverage   91.87%   91.87%   -0.01%     
==========================================
  Files         174      174              
  Lines       50692    50692              
==========================================
- Hits        46575    46571       -4     
- Misses       4117     4121       +4

Flag	Coverage Δ
#multiple	90.41% <ø> (ø)	⬆️
#single	41.78% <ø> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	97% <0%> (-0.12%)	⬇️

---

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[codecov]

Codecov Report

Merging #26643 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26643      +/-   ##
==========================================
- Coverage   91.87%   91.87%   -0.01%     
==========================================
  Files         174      174              
  Lines       50692    50692              
==========================================
- Hits        46575    46571       -4     
- Misses       4117     4121       +4

Flag	Coverage Δ
#multiple	90.41% <ø> (ø)	⬆️
#single	41.78% <ø> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	97% <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 1013706...f0d33af. Read the comment docs.