BUG: StringIO fail import for asv benchmarks

[anmyachev]

• closes N/A
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Fix StringIO import after #25954 PR

[jreback]

lgtm. ping after green on the code checks.

[codecov]

Codecov Report

Merging #25989 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #25989      +/-   ##
==========================================
- Coverage   91.86%   91.85%   -0.01%     
==========================================
  Files         175      175              
  Lines       52543    52543              
==========================================
- Hits        48266    48263       -3     
- Misses       4277     4280       +3

Flag	Coverage Δ
#multiple	90.4% <ø> (ø)	⬆️
#single	41.9% <ø> (-0.08%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	75% <0%> (-12.5%)	⬇️
pandas/core/frame.py	96.79% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.72% <0%> (+0.1%)	⬆️

---

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[codecov]

Codecov Report

Merging #25989 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #25989      +/-   ##
==========================================
- Coverage   91.86%   91.85%   -0.01%     
==========================================
  Files         175      175              
  Lines       52543    52543              
==========================================
- Hits        48266    48263       -3     
- Misses       4277     4280       +3

Flag	Coverage Δ
#multiple	90.4% <ø> (ø)	⬆️
#single	41.9% <ø> (-0.08%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	75% <0%> (-12.5%)	⬇️
pandas/core/frame.py	96.79% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.72% <0%> (+0.1%)	⬆️

---

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 8b15dff...82cbe13. Read the comment docs.

[jreback]

thanks @anmyachev