deps: update maven docker tag to v3.9.12 (GoogleCloudPlatform#4050)

Author: renovate-bot

samples/java/cloud-run/Dockerfile

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 # Use the official maven/Java image to create a build artifact.
-FROM maven:3.9.11-eclipse-temurin-17 as builder
+FROM maven:3.9.12-eclipse-temurin-17 as builder
 
 # Copy local code to the container image.
 WORKDIR /app