build(deps): bump flatpak/flatpak-github-actions from 5 to 6

Bumps [flatpak/flatpak-github-actions](https://github.com/flatpak/flatpak-github-actions) from 5 to 6.
- [Release notes](https://github.com/flatpak/flatpak-github-actions/releases)
- [Commits](https://github.com/flatpak/flatpak-github-actions/compare/v5...v6)

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

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

.github/workflows/release-tip.yml

@@ -47,7 +47,7 @@ jobs:
       with:
         platforms: arm64
 
-    - uses: flatpak/flatpak-github-actions/flatpak-builder@v5
+    - uses: flatpak/flatpak-github-actions/flatpak-builder@v6
       with:
         bundle: ghostty.flatpak
         manifest-path: com.mitchellh.ghostty.yml