[ci] add codecov token to fix random codecov upload failures
[ci] add codecov token to fix random codecov upload failures

e.g. https://github.com/googlefonts/glyphsLib/actions/runs/3218919291/jobs/5263889758#step:7:35

similar to what I did in https://github.com/fonttools/fonttools/issues/2763

I copied the Codecov token from https://app.codecov.io/gh/googlefonts/glyphsLib/settings and pasted into the repository's "secrets".

googlefonts/glyphsLib