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- update outdated GitHub action versions;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>

.github/workflows/android-dockerimage.yml

@@ -15,17 +15,17 @@ jobs:
       VERSION: ${{ '5.15.2' }} # the version numbers here is based on the Qt version, the third digit is the rev of the docker image
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v4
 
     - name: Build the name for the docker image
       id: build_name
       run: |
-        v=${{ env.VERSION }}
-        b=${{ github.ref }} # -BRANCH suffix, unless the branch is master
+        v=$VERSION
+        b=$GITHUB_REF # -BRANCH suffix, unless the branch is master
         b=${b/refs\/heads\//}
         b=${b,,} # the name needs to be all lower case
         if [ $b = "master" ] ; then b="" ; else b="-$b" ; fi
-        echo "NAME=subsurface/android-build${b}:${v}" >> $GITHUB_OUTPUT
+        echo "NAME=$GITHUB_REPOSITORY_OWNER/android-build${b}:${v}" >> $GITHUB_OUTPUT
 
     - name: Build and Publish Linux Docker image to Dockerhub
       uses: elgohr/Publish-Docker-Github-Action@v5