CICD: Improve Workflows.

Make multiple improvements to the existing workflows:
- create a shared custom action to deal with version number tracking
  and generation;
- use this action to add the branch name to the version for pull
  request builds;
- create a shared workflow for all debian-ish builds to avoid re-use
  by copy / paste;
- remove potential security risks by eliminating the use of
  pre-evaluated expressions (`${{ ... }}`) inside scripts;
- update outdated GitHub action versions;
- improve the consistency by renaming scripts acording to have a `.sh`
  extension;
- improve naming of generated artefacts for pull requests to include
  the correct version.

@dirkh: Unfortunately this is potentially going to break builds when it is
merged, as there is no good way to 'test' a merge build short of
merging.
We'll just have to deal with the fallout of it in a follow-up pull
request.

Signed-off-by: Michael Keller <github@ike.ch>

packaging/macosx/make-package.sh

@@ -11,7 +11,7 @@ DMGCREATE=create-dmg
 
 # same git version magic as in the Makefile
 # for the naming of volume and dmg we want the 3 digits of the full version number
-VERSION=$(cd ${DIR}/subsurface; ./scripts/get-version)
+VERSION=$(cd ${DIR}/subsurface; ./scripts/get-version.sh)
 
 # first build and install Subsurface and then clean up the staging area
 # make sure we didn't lose the minimum OS version