Change: Use main branch as target for dependabot updates

Only the main branch will get updates from now on.

.github/dependabot.yml

@@ -2,7 +2,7 @@ version: 2
 updates:
   - package-ecosystem: npm
     directory: '/'
-    target-branch: "stable"
+    target-branch: "main"
     schedule:
       interval: monthly
       time: '04:00'
@@ -47,9 +47,3 @@ updates:
     directory: '/'
     schedule:
       interval: 'weekly'
-
-  - package-ecosystem: 'github-actions'
-    directory: '/'
-    target-branch: "oldstable"
-    schedule:
-      interval: 'weekly'