deps: update dependency com.google.cloud:google-cloud-shared-dependencies to v3.15.0 (googleapis#2615)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-shared-dependencies](https://github.com/googleapis/sdk-platform-java) | `3.14.0` -> `3.15.0` | [![age](https://developer.mend.io/api/mc/badges/age/maven/com.google.cloud:google-cloud-shared-dependencies/3.15.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/maven/com.google.cloud:google-cloud-shared-dependencies/3.15.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/maven/com.google.cloud:google-cloud-shared-dependencies/3.14.0/3.15.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/maven/com.google.cloud:google-cloud-shared-dependencies/3.14.0/3.15.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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Author: renovate-bot

pom.xml

@@ -54,7 +54,7 @@
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     <github.global.server>github</github.global.server>
     <site.installationModule>google-cloud-spanner-parent</site.installationModule>
-    <google.cloud.shared-dependencies.version>3.14.0</google.cloud.shared-dependencies.version>
+    <google.cloud.shared-dependencies.version>3.15.0</google.cloud.shared-dependencies.version>
   </properties>
 
   <dependencyManagement>