chore: Update dependabot.yml template (#1813)

* chore: Update `dependabot.yml` template not to touch pip dependencies
Source-Link: googleapis/synthtool@f961eb0
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:af2eda87a54601ae7b7b2be5055c17b43ac98a7805b586772db314de8a7d4a1d

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,4 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:ad9cabee4c022f1aab04a71332369e0c23841062124818a4490f73337f790337
+  digest: sha256:af2eda87a54601ae7b7b2be5055c17b43ac98a7805b586772db314de8a7d4a1d
+# created: 2023-06-16T02:10:09.149325782Z

.github/dependabot.yml

@@ -5,10 +5,13 @@ updates:
     schedule:
       interval: "daily"
     # Disable version updates for Maven dependencies
-    open-pull-requests-limit: 0
+    # we use renovate-bot as well as shared-dependencies BOM to update maven dependencies.
+    ignore: "*"
   - package-ecosystem: "pip"
     directory: "/"
     schedule:
       interval: "daily"
     # Disable version updates for pip dependencies
-    open-pull-requests-limit: 0
+    # If a security vulnerability comes in, we will be notified about 
+    # it via template in the synthtool repository.
+    ignore: "*"