build: upgrade codecov-action and disable failing_ci_if_error

[ktmud]

🏠 Internal

Codecov uploads have been failing for no reason (because of missing GITHUB_ACTION env variables).

Trying to fix it by:

1. Fix to build on ubuntu-18.04
2. Manually add GITHUB_ACTION and CODECOV_TOKEN env variables.

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[ktmud]

So it seems codecov has stopped working for all GitHub Actions. I'll merge this one to just to let the CI pass.

[codecov]

Codecov Report

Merging #723 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #723   +/-   ##
=======================================
  Coverage   24.19%   24.19%           
=======================================
  Files         339      339           
  Lines        7617     7617           
  Branches      925      925           
=======================================
  Hits         1843     1843           
  Misses       5701     5701           
  Partials       73       73           

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