readme.md: update GitHub actions status badges

[alexandear]

According to the doc a workflow status badge must have syntax:

https://github.com/danmar/cppcheck/actions/workflows/<WORKFLOW_FILE>/badge.svg

So, changed readme.md to the following:

GitHub Actions	OSS-Fuzz	Coverity Scan Build Status	License

[firewave]

Thanks for your contribution.

Looking at this I wonder if the "GitHub Actions" part still makes sense.
Development is mostly done via PRs and we only merge them if all builds pass. So even if a direct push to the main branch causes it to break that needs to be resolved immediately as it would break any PR. So those badges provide no useful information as they are virtually always green.

Having a badge for code coverage would be much better (not sure if we can get that out of codecov). And as it is something which we don't actively follow up on it would also be helpful.

I am trying to think any other badges to use but that would have to be some metric which comes from an external source. Any suggestions/thoughts?

[firewave]

@danmar https://docs.codecov.com/docs/status-badges
I am not able to access the badge part of the settings.

Some notes on the coverage data:

• we need to exclude the test sources as well as tinyxml2 and picojson from the coverage. simplecpp should stay as we are partially acting as the actual tests for it.
• it seems like master is still configured as the default/primary branch but it should be main

[alexandear]

Having a badge for code coverage would be much better

Agree.

Anyway, we should definitely fix the current not working badge "GitHub Actions Status":

[danmar]

I am not able to access the badge part of the settings.

me neither directly. can we wait with that a little.

[alexandear]

So, should I need to close this PR?

[danmar]

I think you should remove the CI-cygwin](https://github.com/danmar/cppcheck/actions/workflows/CI-cygwin.yml/badge.svg etc