chore(main): release 2.3.1-SNAPSHOT (#497)

🤖 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]

java-grafeas/pom.xml

@@ -5,7 +5,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>io.grafeas</groupId>
   <artifactId>grafeas</artifactId>
-  <version>2.3.0</version><!-- {x-version-update:grafeas:current} -->
+  <version>2.3.1-SNAPSHOT</version><!-- {x-version-update:grafeas:current} -->
   <packaging>jar</packaging>
   <name>Grafeas Client</name>
   <url>https://github.com/googleapis/google-cloud-java/tree/master/google-cloud-clients/grafeas

java-grafeas/versions.txt

@@ -1,4 +1,4 @@
 # Format:
 # module:released-version:current-version
 
-grafeas:2.3.0:2.3.0
+grafeas:2.3.0:2.3.1-SNAPSHOT