WIP codecov: update to v3 action

[imirkin]

v1 is deprecated and no longer works. Update to v3.

Fixes #743

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (develop/v2@851d370). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             develop/v2     #778   +/-   ##
=============================================
  Coverage              ?   70.91%           
=============================================
  Files                 ?       90           
  Lines                 ?    13173           
  Branches              ?        0           
=============================================
  Hits                  ?     9341           
  Misses                ?     3016           
  Partials              ?      816           

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[imirkin]

Hmmmm ... unclear if this helps. The earlier PRs also had accurate numbers for that PR but not the baseline... also should probably only upload a single tag's worth of coverage.

Please consider this WIP.

[imirkin]

Ah no ... looks like v1 isn't as gone as the docs make it out to be. For some reason it's looking at the wrong thing for the parent, probably needs some settings in codecov but I probably am not allowed to do it or can't figure out how. Or ... something else. In any case, no clue how to fix.

[lestrrat]

Me neither! :D