chore: Update monitoring to the latest version

Author: lqiu96

java-datastore/google-cloud-datastore/pom.xml

@@ -204,12 +204,12 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-monitoring</artifactId>
-      <version>3.90.0</version><!-- {x-version-update:google-cloud-monitoring:current} -->
+      <version>3.91.0</version><!-- {x-version-update:google-cloud-monitoring:current} -->
     </dependency>
     <dependency>
       <groupId>com.google.api.grpc</groupId>
       <artifactId>proto-google-cloud-monitoring-v3</artifactId>
-      <version>3.90.0</version><!-- {x-version-update:google-cloud-monitoring:current} -->
+      <version>3.91.0</version><!-- {x-version-update:google-cloud-monitoring:current} -->
     </dependency>
     <dependency>
       <groupId>io.opentelemetry</groupId>