fix(java-cloud-bom): fix parent relative path in validate-bom

Author: jinseopkim0

java-cloud-bom/tests/validate-bom/pom.xml

@@ -7,7 +7,7 @@
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-pom-parent</artifactId>
     <version>1.88.0-SNAPSHOT</version><!-- {x-version-update:google-cloud-java:current} -->
-    <relativePath>../../google-cloud-pom-parent/pom.xml</relativePath>
+    <relativePath>../../../google-cloud-pom-parent/pom.xml</relativePath>
   </parent>
   <modelVersion>4.0.0</modelVersion>