chore: Add opentelemetry-sdk-metrics as test-scope dep

Author: lqiu96

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

@@ -213,6 +213,11 @@
       <artifactId>opentelemetry-sdk-trace</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>io.opentelemetry</groupId>
+      <artifactId>opentelemetry-sdk-metrics</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>io.opentelemetry</groupId>
       <artifactId>opentelemetry-semconv</artifactId>