Activate dependabot on maven-4.0.x branch (#2535)

Author: gnodet

.github/dependabot.yml

@@ -22,6 +22,15 @@ updates:
     schedule:
       interval: "daily"
 
+  - package-ecosystem: "maven"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    target-branch: "maven-4.0.x"
+    labels:
+      - "mvn40"
+      - "dependencies"
+
   - package-ecosystem: "maven"
     directory: "/"
     schedule:
@@ -36,6 +45,15 @@ updates:
     schedule:
       interval: "daily"
 
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    target-branch: "maven-4.0.x"
+    labels:
+      - "mvn40"
+      - "dependencies"
+
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: