ci: Update for switch to fd.o 22.08 runtime

Part-of: <https://gitlab.gnome.org/GNOME/fractal/-/merge_requests/1144>

.gitlab-ci.yml

@@ -136,7 +136,7 @@ pages:
   tags:
     - flatpak
   script:
-    - flatpak install --user --noninteractive org.freedesktop.Sdk.Extension.rust-nightly//22.08beta
+    - flatpak install --user --noninteractive org.freedesktop.Sdk.Extension.rust-nightly//22.08
     - sed -i 's|rust-stable|rust-nightly|g' ${MANIFEST_PATH}
     - flatpak-builder --keep-build-dirs --user --disable-rofiles-fuse --stop-at=${FLATPAK_MODULE} flatpak_app --repo=repo ${BRANCH:+--default-branch=$BRANCH} ${MANIFEST_PATH}
     - echo "ninja src/doc" | flatpak-builder --disable-rofiles-fuse --build-shell=${FLATPAK_MODULE} flatpak_app ${MANIFEST_PATH}