Revert to simple HTTPS cloning for public repos

- Use Forgejo checkout action with HTTPS (no SSH)
- Update submodule URLs from SSH to HTTPS
- All repos are now public, no authentication needed

.gitmodules

@@ -12,7 +12,7 @@
 	url = https://github.com/FreeCAD/AddonManager.git
 [submodule "mods/ztools"]
 	path = mods/ztools
-	url = git@gitea.kindred.internal:kindred/ztools-0065.git
+	url = https://gitea.kindred.internal/kindred/ztools-0065.git
 [submodule "mods/silo"]
 	path = mods/silo
-	url = git@gitea.kindred.internal:kindred/silo-0062.git
+	url = https://gitea.kindred.internal/kindred/silo-0062.git