CI and Flatpak: Use the 3.28 runtime till fdo 1.8 is fixed.

.gitlab-ci.yml

@@ -55,7 +55,7 @@ rust:nightly:
         - web
 
 flatpak:
-    image: registry.gitlab.gnome.org/gnome/gnome-nightly-oci/rust-bundle:latest
+    image: registry.gitlab.gnome.org/gnome/gnome-runtime-images/rust_bundle:3.28
     stage: test
     script:
         - flatpak-builder --stop-at=hammond app org.gnome.Hammond.json

org.gnome.Hammond.json

@@ -1,7 +1,7 @@
 {
     "app-id" : "org.gnome.Hammond",
     "runtime" : "org.gnome.Platform",
-    "runtime-version" : "master",
+    "runtime-version" : "3.28",
     "sdk" : "org.gnome.Sdk",
     "sdk-extensions" : [
         "org.freedesktop.Sdk.Extension.rust-stable"