chore: release 0.121.6-SNAPSHOT (#605)

🤖 I have created a release \*beep\* \*boop\*
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### Updating meta-information for bleeding-edge SNAPSHOT release.
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This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

errorreporting/snapshot/pom.xml

@@ -28,7 +28,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-errorreporting</artifactId>
-      <version>0.121.5-beta</version>
+      <version>0.121.6-beta-SNAPSHOT</version>
     </dependency>
     <!-- {x-version-update-end} -->