chore(deps): bump bilelmoussaoui/flatpak-github-actions from 3 to 4

Bumps [bilelmoussaoui/flatpak-github-actions](https://github.com/bilelmoussaoui/flatpak-github-actions) from 3 to 4.
- [Release notes](https://github.com/bilelmoussaoui/flatpak-github-actions/releases)
- [Commits](https://github.com/bilelmoussaoui/flatpak-github-actions/compare/v3...v4)

---
updated-dependencies:
- dependency-name: bilelmoussaoui/flatpak-github-actions
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build_flatpak.yml

@@ -23,7 +23,7 @@ jobs:
       - uses: actions/checkout@v2.3.4
         with:
           submodules: true
-      - uses: bilelmoussaoui/flatpak-github-actions/flatpak-builder@v3
+      - uses: bilelmoussaoui/flatpak-github-actions/flatpak-builder@v4
         with:
           cache-key: flatpak-builder-${{ github.sha }}
           bundle: "soundux.flatpak"