Add support for Github Actions build number

[rand0m86]

Describe the idea (required)

Currently there is no support for build number in Github Actions integration. Maybe it was not that straightforward at a time when the plugin was created.
Now it seems quite trivial, we simply have to take value from GITHUB_RUN_NUMBER environment variable.
See https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/store-information-in-variables.

Tell us about the expected behaviour (required)

It is expected to get build.number variable in the plugin populated.

Context (optional)

See PR git-commit-id/git-commit-id-plugin-core#228

[TheSnoozer]

Thanks for creating an issue here!
Let's continue the discussion in the PR :-)

[TheSnoozer]

Thanks again for your contribution!
This should become available with the update to the latest core-version (#850)

[rand0m86]

Thanks, I'll wait for version 9.0.2 of maven plugin.

[TheSnoozer]

It's available now: https://repo1.maven.org/maven2/io/github/git-commit-id/git-commit-id-maven-plugin/9.0.2/ :-)

[rand0m86]

Thanks again, it was super quick 🙂