CI/Flatpak: Switch from JSON -> YAML

Actually lets me have comments...

scripts/flatpak/modules/25-discord-rpc.yaml

@@ -0,0 +1,20 @@
+name: discord-rpc
+buildsystem: cmake-ninja
+builddir: true
+config-opts:
+  - "-DCMAKE_BUILD_TYPE=Release"
+  - "-DBUILD_SHARED_LIBS=ON"
+build-options:
+  strip: true
+sources:
+  - type: git
+    url: "https://github.com/stenzek/discord-rpc.git"
+    commit: "144f3a3f1209994d8d9e8a87964a989cb9911c1e"
+cleanup:
+  - /bin
+  - /include
+  - /lib/*.a
+  - /lib/*.la
+  - /lib/cmake
+  - /lib/pkgconfig
+  - /share