GHA master/develop coverage

[sdarwin]

• code-coverage.yml GHA
• run on pushes to master or develop
• curl lcov-jenkins-gcc-13.sh
• Detour: add --flags to lcov-jenkins-gcc-13.sh to optionally skip some other output sections, and therefore only invoke gcovr
• run lcov-jenkins-gcc-13.sh
• switch to another directory. Check out or create a code-coverage branch.
• create develop/master subdirectories
• dump a basic html text file index.html with links to develop and master
• copy the previously generated gcovr results here
• git add, commit, push, to the code-coverage branch
• The result being that the has contents:

index.html
master/
develop/

with coverage results in the directories.
Host on github pages