deps: minor cleanup (#2623)

* use mockito bom
* stop using scopes in dep management

Change-Id: I79ac199199b90ea8320d1a70ddef029cd3380dc1

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Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: igorbernstein2

pom.xml

@@ -190,7 +190,6 @@
                 <groupId>com.google.truth.extensions</groupId>
                 <artifactId>truth-proto-extension</artifactId>
                 <version>1.4.4</version>
-                <scope>test</scope>
                 <exclusions>
                     <!-- exclude protobuf-java as it is managed in the shared deps bom-->
                     <exclusion>
@@ -206,8 +205,10 @@
             </dependency>
             <dependency>
                 <groupId>org.mockito</groupId>
-                <artifactId>mockito-core</artifactId>
+                <artifactId>mockito-bom</artifactId>
                 <version>4.11.0</version>
+                <type>pom</type>
+                <scope>import</scope>
             </dependency>
         </dependencies>
     </dependencyManagement>