CI: Let github workflow use version number in the flatpak filename

Note: For pull requests, the version that is tested is an autogenerated
temporary merge commit (which is good, since it tests whether things
work *after* merging), but that commit id is also included in the
filename which might be bit suprising. To be considered later.

.github/workflows/testing.yml

@@ -82,6 +82,10 @@ jobs:
     steps:
       - name: Prepare repo
         uses: actions/checkout@v2
+        # Fetch history, so we also fetch the previous tag for deriving
+        # the version number
+        with:
+          fetch-depth: 0
       - name: Install system packages
         # It would be good to cache the GNOME Sdk, as it
         # is rather big to download each time.
@@ -105,10 +109,14 @@ jobs:
       - name: Export bundle and try to install it
         run: |
           mkdir -p dist
-          flatpak build-bundle --runtime-repo=https://flathub.org/repo/flathub.flatpakrepo build/flatpak/repo dist/Hamster.flatpak org.gnome.Hamster
-          flatpak --user -y install dist/Hamster.flatpak
+          # Note: For pull requests, this version includes the git hash
+          # of the autogenerated *merge* commit, not the original
+          # to-be-merged commit (because that's also what is tested).
+          VERSION=$(python src/hamster/version.py)
+          flatpak build-bundle --runtime-repo=https://flathub.org/repo/flathub.flatpakrepo build/flatpak/repo "dist/Hamster-$VERSION.flatpak" org.gnome.Hamster
+          flatpak --user -y install "dist/Hamster-$VERSION.flatpak"
       - name: Upload built artifact
         uses: actions/upload-artifact@v2
         with:
           name: Flatpak application
-          path: dist/Hamster.flatpak
+          path: dist/*.flatpak