Use Pipx Install Action to Install Gcovr

[threeal]

This issue suggests utilizing the Pipx Install Action to install gcovr using pipx on GitHub Actions. This change will replace the @actions-kit/pip package that was previously utilized for installing gcovr using pip.

To utilize the Pipx Install Action before that package is released, we can use the dist branch of that repository, which contains the compiled source. This way, it can be directly included using the GitHub URL.