test: prevent root versions.txt from affecting postprocessor test fixtures

After the monorepo migration, the shared versions.txt at the root caused Release Please to mutate test fixtures named pom.xml, breaking the postprocessor unit test.

- Added -golden suffix to version markers in test resources to isolate them from Release Please scanning.

Fixes #12841

Author: meltsufin

sdk-platform-java/hermetic_build/library_generation/tests/resources/test_monorepo_postprocessing/java-dns/pom.xml

@@ -4,6 +4,6 @@
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-dns</artifactId>
   <packaging>jar</packaging>
-  <version>2.33.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-dns:current} -->
+  <version>2.33.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-dns-golden:current} -->
   <name>Google Cloud DNS Parent</name>
 </project>

sdk-platform-java/hermetic_build/library_generation/tests/resources/test_monorepo_postprocessing/java-service-control/google-cloud-service-control-bom/pom.xml

@@ -3,6 +3,6 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-service-control-bom</artifactId>
-  <version>1.35.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-service-control:current} -->
+  <version>1.35.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-service-control-golden:current} -->
   <packaging>pom</packaging>
 </project>

sdk-platform-java/hermetic_build/library_generation/tests/resources/test_monorepo_postprocessing/java-tasks/google-cloud-tasks-bom/pom.xml

@@ -3,6 +3,6 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-tasks-bom</artifactId>
-  <version>2.35.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-tasks:current} -->
+  <version>2.35.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-tasks-golden:current} -->
   <packaging>pom</packaging>
 </project>