CI: don't specify google-auth

[jreback]

xref googleapis/python-bigquery-pandas#271

appears latest google-cloud-bigquery is causing issues.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@9fbb9e7). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #25994   +/-   ##
=========================================
  Coverage          ?   91.81%           
=========================================
  Files             ?      175           
  Lines             ?    52549           
  Branches          ?        0           
=========================================
  Hits              ?    48250           
  Misses            ?     4299           
  Partials          ?        0

Flag	Coverage Δ
#multiple	90.38% <ø> (?)
#single	40.72% <ø> (?)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@9fbb9e7). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #25994   +/-   ##
=========================================
  Coverage          ?   91.81%           
=========================================
  Files             ?      175           
  Lines             ?    52549           
  Branches          ?        0           
=========================================
  Hits              ?    48250           
  Misses            ?     4299           
  Partials          ?        0

Flag	Coverage Δ
#multiple	90.38% <ø> (?)
#single	40.72% <ø> (?)

---

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 9fbb9e7...9a4763a. Read the comment docs.