CLN: replace %s syntax with .format in core.indexing and core.internals

[AaronCritchley]

• Progress towards CLN: replace %s formatting syntax with .format #16130
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff

[AaronCritchley]

Is this supposed to be 'smaller itemsize than current'? If yes, would you like me to change in this PR?

[jreback]

yes

[codecov]

Codecov Report

Merging #18331 into master will decrease coverage by 0.01%.
The diff coverage is 76.19%.

@@            Coverage Diff             @@
##           master   #18331      +/-   ##
==========================================
- Coverage   91.38%   91.36%   -0.02%     
==========================================
  Files         164      164              
  Lines       49780    49790      +10     
==========================================
+ Hits        45491    45492       +1     
- Misses       4289     4298       +9

Flag	Coverage Δ
#multiple	89.17% <76.19%> (ø)	⬆️
#single	39.49% <4.76%> (-0.06%)	⬇️

Impacted Files	Coverage Δ
pandas/core/indexing.py	92.8% <0%> (ø)	⬆️
pandas/core/internals.py	94.54% <80%> (ø)	⬆️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️
pandas/core/generic.py	95.73% <0%> (ø)	⬆️
pandas/core/series.py	95.02% <0%> (+0.01%)	⬆️
pandas/core/sparse/series.py	95.33% <0%> (+0.05%)	⬆️

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[jreback]

lgtm. ping when green (after than tiny change).

[AaronCritchley]

@jreback last build green, change made to the error message as discussed 😄

[jreback]

thanks!