Fix handling of error output

[afshin]

Follow up to #77, addresses error seen in publish workflow

[codecov-commenter]

Codecov Report

Merging #79 (4aff85d) into master (5b17742) will decrease coverage by 3.84%.
The diff coverage is 69.30%.

@@            Coverage Diff             @@
##           master      #79      +/-   ##
==========================================
- Coverage   89.03%   85.19%   -3.85%     
==========================================
  Files          15       16       +1     
  Lines        1697     1898     +201     
  Branches      198      239      +41     
==========================================
+ Hits         1511     1617     +106     
- Misses        118      190      +72     
- Partials       68       91      +23     

Impacted Files	Coverage Δ
jupyter_releaser/actions/draft_release.py	0.00% <0.00%> (ø)
jupyter_releaser/util.py	69.87% <46.87%> (-15.02%)	⬇️
jupyter_releaser/changelog.py	88.18% <62.50%> (-2.56%)	⬇️
jupyter_releaser/lib.py	74.28% <67.39%> (-3.46%)	⬇️
jupyter_releaser/npm.py	80.14% <70.37%> (-3.60%)	⬇️
jupyter_releaser/tests/test_cli.py	96.46% <76.92%> (-1.38%)	⬇️
jupyter_releaser/tee.py	82.05% <82.05%> (ø)
jupyter_releaser/__init__.py	100.00% <100.00%> (ø)
jupyter_releaser/cli.py	92.37% <100.00%> (+0.13%)	⬆️
jupyter_releaser/python.py	91.66% <100.00%> (+3.78%)	⬆️
... and 4 more

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