deps: update dependency com.google.cloud:google-cloud-core to v2.1.5 (#685)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-core](https://togithub.com/googleapis/java-core) | `2.1.4` -> `2.1.5` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.1.5/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.1.5/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.1.5/compatibility-slim/2.1.4)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.1.5/confidence-slim/2.1.4)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>googleapis/java-core</summary>

### [`v2.1.5`](https://togithub.com/googleapis/java-core/blob/master/CHANGELOG.md#&#8203;215-httpswwwgithubcomgoogleapisjava-corecomparev214v215-2021-09-21)

[Compare Source](https://togithub.com/googleapis/java-core/compare/v2.1.4...v2.1.5)

</details>

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Author: renovate-bot

errorreporting/install-without-bom/pom.xml

@@ -36,7 +36,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.1.4</version>
+      <version>2.1.5</version>
     </dependency>
     <dependency>
       <groupId>junit</groupId>

errorreporting/snapshot/pom.xml

@@ -35,7 +35,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.1.4</version>
+      <version>2.1.5</version>
     </dependency>
     <dependency>
       <groupId>junit</groupId>