let Dependabot use a single "dependencies" label only

.github/dependabot.yml

@@ -4,6 +4,8 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+    labels:
+      - "dependencies"
 
   - package-ecosystem: "pip"
     directory: "/"
@@ -12,3 +14,5 @@ updates:
     ignore:
       - dependency-name: "*"
         update-types: ["version-update:semver-patch"]
+    labels:
+      - "dependencies"