docs ci: add 0.4 release

Author: bilelmoussaoui

.github/workflows/docs.yml

@@ -16,6 +16,7 @@ jobs:
       image: ghcr.io/gtk-rs/gtk4-rs/gtk4:latest
     env:
       RELEASES: |
+        0.4=0.4
         0.3=0.3
         0.2=0.2
         0.1=0.1