build: Update appropriate branches to stable and CI image

.gitlab-ci.yml

@@ -81,7 +81,7 @@ ubuntu:
     expire_in: 2 days
 
 flatpak:
-  image: 'registry.gitlab.gnome.org/gnome/gnome-runtime-images/gnome:master'
+  image: 'registry.gitlab.gnome.org/gnome/gnome-runtime-images/gnome:3.38'
   variables:
     APP_ID: org.gnome.Geary.Devel
     FLATPAK_MODULE: geary

org.gnome.Geary.yaml

@@ -14,7 +14,7 @@
 app-id: org.gnome.Geary.Devel
 branch: master
 runtime: org.gnome.Platform
-runtime-version: master
+runtime-version: "3.38"
 sdk: org.gnome.Sdk
 command: geary
 
@@ -152,7 +152,7 @@ modules:
     sources:
       - type: git
         url: https://gitlab.gnome.org/GNOME/evolution-data-server.git
-        branch: master
+        branch: gnome-3-38
     cleanup:
       - /lib/cmake
       - /lib/evolution-data-server/*-backends
@@ -242,4 +242,4 @@ modules:
     sources:
       - type: git
         url: https://gitlab.gnome.org/GNOME/geary.git
-        branch: mainline
+        branch: gnome-3-38