Autobuild: Clean up redundant variables in workflow definition

[hoffie]

Short description of changes

• Autobuild: Don't hardcode python path in analyse_git_reference.py

• Autobuild: Move Changelog generation to the workflow
  Previously, the autobuild changelog (autoLatestChangelog.md) which is used for the Github release body, was generated as part of the "analyse_git_reference.py" script. It does not seem logical for an analysis script to have a side effect of producing a Changelog file. Also, the file name (autoLatestChangelog.md) was hardcoded in two places and had to match (workflow + script).
  With this commit, the changelog generation call (.github/actions_scripts/getChangelog.pl) is moved to the workflow. This follows the principle of least surprise and moves the output file name usage to a single file (the workflow).

• Autobuild: Improve variable naming/coding style in analyse_git_reference.py

• Autobuild: Move .github/action_scripts to .github/autobuild
  This also renames the two scripts to better reflect what they do.

• Autobuild: Drop redundant github.workspace variable reference in workflow

Edit: This PR lacked most of the changes above. See #2656 for a re-submission with the missing parts.

CHANGELOG: (Autobuild: Clean up redundant variables in workflow definition; to be condensed with other Autobuild refactoring entries)

Context: Fixes an issue?

I think it had been mentioned elsewhere

• that .github/action_scripts/* should be moved to .github/autobuild/ instead, as that's where they are used now
• that an analyze_something script is not supposed to have the side effect of writing a (Changelog) file

Does this change need documentation? What needs to be documented and how?

No.

Status of this Pull Request

Ready.

What is missing until this pull request can be merged?

Reviews.

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want:
• Build is still green
• Release/changelog logic still works: https://github.com/hoffie/jamulus/releases/tag/r0_0_1devHoffieTest
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

[ann0see]

Looks sane.

[hoffie]

Somehow this PR lost most of the supposed content before merge (maybe due to a bad rebase). I'll re-submit what's left.