CI/Flatpak: Switch from JSON -> YAML

Actually lets me have comments...

scripts/flatpak/modules/21-libbacktrace.yaml

@@ -0,0 +1,14 @@
+name: libbacktrace
+buildsystem: autotools
+no-autogen: true
+build-options:
+  strip: false
+  no-debuginfo: true
+sources:
+  - type: git
+    url: "https://github.com/ianlancetaylor/libbacktrace.git"
+    commit: "ad106d5fdd5d960bd33fae1c48a351af567fd075"
+cleanup:
+  - /include
+  - /lib/*.a
+  - /lib/*.la