deps: update dependency com.google.cloud:google-cloud-notification to v0.123.9-beta (#4951)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-notification](https://togithub.com/googleapis/java-notification) | `0.123.8-beta` -> `0.123.9-beta` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-notification/0.123.9-beta/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-notification/0.123.9-beta/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-notification/0.123.9-beta/compatibility-slim/0.123.8-beta)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-notification/0.123.9-beta/confidence-slim/0.123.8-beta)](https://docs.renovatebot.com/merge-confidence/) |

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google-cloud-bom/pom.xml

@@ -585,7 +585,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-notification</artifactId>
-        <version>0.123.8-beta</version>
+        <version>0.123.9-beta</version>
       </dependency>
       <dependency>
         <groupId>com.google.cloud</groupId>