CI: add 0.3 release

This should fix the too old release we get in the 0.3 docs

Author: bilelmoussaoui

.github/workflows/docs.yml

@@ -15,6 +15,7 @@ jobs:
       image: ghcr.io/gtk-rs/gtk4-rs/gtk4:latest
     env:
       RELEASES: |
+        0.3=0.3
         0.2=0.2
         0.1=0.1
     steps: