TST: fix up pandas_datareader downstream tests

[jreback]

closes #18935

[codecov]

Codecov Report

Merging #19490 into master will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #19490      +/-   ##
==========================================
+ Coverage   91.67%   91.77%   +0.09%     
==========================================
  Files         148      148              
  Lines       48542    49170     +628     
==========================================
+ Hits        44501    45124     +623     
- Misses       4041     4046       +5

Flag	Coverage Δ
#multiple	90.13% <ø> (+0.09%)	⬆️
#single	41.99% <ø> (+0.27%)	⬆️

Impacted Files	Coverage Δ
pandas/io/pytables.py	92.61% <0%> (+0.16%)	⬆️
pandas/io/formats/format.py	96.57% <0%> (+0.32%)	⬆️
pandas/io/parsers.py	96.21% <0%> (+0.71%)	⬆️

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