use only maven central for dependabot

Signed-off-by: Olivier Lamy <olamy@apache.org>
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 1cc272f..d969d0a 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -16,9 +16,17 @@
 # under the License.
 
 version: 2
+
+registries:
+  maven-central:
+    type: maven-repository
+    url: https://repo.maven.apache.org/maven2
+
 updates:
   - package-ecosystem: "maven"
     directory: "/"
+    registries:
+      - maven-central
     schedule:
       interval: "daily"