CLN: Rename raise_on_error to errors for .dtype

[gfyoung]

Title is self-explanatory.

xref #14967.

[pep8speaks]

Hello @gfyoung! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/generic.py !

• There are no PEP8 issues in the file pandas/tests/frame/test_dtypes.py !

• There are no PEP8 issues in the file pandas/tests/series/test_dtypes.py !

[codecov]

Codecov Report

Merging #23374 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #23374      +/-   ##
==========================================
- Coverage   92.22%   92.22%   -0.01%     
==========================================
  Files         169      169              
  Lines       51261    51260       -1     
==========================================
- Hits        47277    47276       -1     
  Misses       3984     3984

Flag	Coverage Δ
#multiple	90.66% <100%> (-0.01%)	⬇️
#single	42.22% <100%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/generic.py	96.79% <100%> (-0.01%)	⬇️

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[jreback]

thanks!