ci: reworked windows builds

[sergiud]

Closes #735

[coveralls]

Coverage decreased (-4.8%) to 71.852% when pulling 840b520 on ci-win32-builds into 503e3de on master.

[sergiud]

@drigz I've been trying to fix merging of multiple coverage reports (mainly MinGW and Linux) over the the past weeks. However, this turned out to be very tricky due to the way both Coveralls and Github workflows work. Since the Github workflows are defined in separate files, merging the reports cannot be done automatically and requires additional logic which is not straightforward to implement. Additionally, Coveralls seems to have problems parsing MinGW coverage reports (a 0% coverage is always reported).

At this point, I believe switching to Codecov is a better solution in the long-term.

[drigz]

LGTM. Let me know if you need any action from me to enable Codecov.

[sergiud]

Thanks. We would need a CODECOV_TOKEN secret with Codecov token assigned to it as detailed here. Coveralls bot access to repo can be revoked.

[drigz]

Where would we store the CODECOV_TOKEN? Assuming we wouldn't be manually uploading coverage data, it's not clear how it should be used. It also says "Note: Token not required for public repositories uploading from Travis, CircleCI, AppVeyor, Azure Pipelines or GitHub Actions." - does this apply to us?

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (master@503e3de). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #737   +/-   ##
=========================================
  Coverage          ?   71.38%           
=========================================
  Files             ?       17           
  Lines             ?     3208           
  Branches          ?        0           
=========================================
  Hits              ?     2290           
  Misses            ?      918           
  Partials          ?        0           

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[sergiud]

I obviously ignored that note, thanks. The token does not seem to be necessary.