Minor: tox: coverage: use -m with coverage-report

[blueyed]

No description provided.

[codecov]

Codecov Report

Merging #5427 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5427   +/-   ##
=======================================
  Coverage   95.98%   95.98%           
=======================================
  Files         114      114           
  Lines       25502    25502           
  Branches     2479     2479           
=======================================
  Hits        24479    24479           
  Misses        717      717           
  Partials      306      306

Impacted Files	Coverage Δ
src/_pytest/_code/code.py	94.32% <ø> (ø)	⬆️

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[asottile]

+0 -- seems fine -- thanks!

[blueyed]

Hmm, py37 on Azure failed to upload coverage:

…
TOTAL                                      25503   1335   4967    345    94%
+ bash /dev/fd/63 -Z -X gcov -X coveragepy -X search -X xcode -X gcovout -X fix -f coverage.xml
++ curl -s https://codecov.io/bash
##[section]Finishing: Report and upload coverage

Restarted.