deps: update dependency com.google.cloud:google-cloud-pubsub-bom to v1.123.8 (#5909)

Author: renovate-bot

google-cloud-bom/pom.xml

@@ -281,7 +281,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-pubsub-bom</artifactId>
-        <version>1.123.7</version>
+        <version>1.123.8</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>