Bump flatpak/flatpak-github-actions from 6.5 to 6.6

Bumps [flatpak/flatpak-github-actions](https://github.com/flatpak/flatpak-github-actions) from 6.5 to 6.6.
- [Release notes](https://github.com/flatpak/flatpak-github-actions/releases)
- [Commits](flatpak/flatpak-github-actions@v6.5...v6.6)

---
updated-dependencies:
- dependency-name: flatpak/flatpak-github-actions
  dependency-version: '6.6'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Build
-        uses: flatpak/flatpak-github-actions/flatpak-builder@v6.5
+        uses: flatpak/flatpak-github-actions/flatpak-builder@v6.6
         with:
           bundle: code.flatpak
           manifest-path: io.elementary.code.yml