Fix coverage upload

[blink1073]

We were getting the error:

==> Detecting CI provider
GitHub Actions CI Detected
Fixing merge commit SHA
==> Preparing upload
==> Processing gcov (disable by -X gcov)
==> Collecting reports
Generating coverage xml reports for Python
Error running `['/Users/runner/hostedtoolcache/Python/3.8.14/x64/bin/python', '-m', 'coverage', 'xml', '-i']`: returncode=1, output=b"Can't read 'pyproject.toml' without TOML support. Install with [toml] extra\n"
- Ignored: [Errno 2] No such file or directory: '/Users/runner/work/jupyter_server/jupyter_server/coverage.xml'
Error: No coverage report found
Tip: See all example repositories: https://github.com/codecov?query=example

https://github.com/jupyter-server/jupyter_server/actions/runs/3536103578/jobs/5934829302

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.39%. Comparing base (a763da3) to head (4f140c3).
Report is 274 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1091      +/-   ##
==========================================
+ Coverage   79.35%   79.39%   +0.03%     
==========================================
  Files          68       68              
  Lines        8294     8294              
  Branches     1649     1652       +3     
==========================================
+ Hits         6582     6585       +3     
+ Misses       1285     1284       -1     
+ Partials      427      425       -2     

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