Dependabot should use Eclipse Maven repository (#61)

This was forgotten in commit 5d2876d
and without this change it fails with following error:

    The property '#/registries' includes the "eclipse" registry which is not used in any of the configurations

.github/dependabot.yml

@@ -6,6 +6,7 @@ registries:
 updates:
   - package-ecosystem: "github-actions"
     directory: "/"
+    registries: "*"
     schedule:
       interval: "weekly"
     labels: