chore: release 0.121.9-SNAPSHOT (#492)

🤖 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).

Author: release-please[bot]

pom.xml

@@ -5,7 +5,7 @@
   <modelVersion>4.0.0</modelVersion>
 
   <artifactId>google-cloud-logging-logback</artifactId>
-  <version>0.121.8-alpha</version><!-- {x-version-update:google-cloud-logging-logback:current} -->
+  <version>0.121.9-alpha-SNAPSHOT</version><!-- {x-version-update:google-cloud-logging-logback:current} -->
   <packaging>jar</packaging>
   <name>Google Cloud Logging Logback Appender</name>
   <url>https://github.com/googleapis/java-logging-logback</url>

versions.txt

@@ -1,4 +1,4 @@
 # Format:
 # module:released-version:current-version
 
-google-cloud-logging-logback:0.121.8-alpha:0.121.8-alpha
+google-cloud-logging-logback:0.121.8-alpha:0.121.9-alpha-SNAPSHOT