deps: update dependency com.google.cloud:google-iam-policy to v1.6.15 (#539)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-iam-policy](https://togithub.com/googleapis/java-eventarc) ([source](https://togithub.com/googleapis/java-iam)) | `1.6.14` -> `1.6.15` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-iam-policy/1.6.15/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-iam-policy/1.6.15/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-iam-policy/1.6.15/compatibility-slim/1.6.14)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-iam-policy/1.6.15/confidence-slim/1.6.14)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v1.6.15`](https://togithub.com/googleapis/java-iam/blob/HEAD/CHANGELOG.md#&#8203;1615-httpsgithubcomgoogleapisjava-iamcomparev1614v1615-2022-11-18)

[Compare Source](https://togithub.com/googleapis/java-iam/compare/v1.6.14...v1.6.15)

##### Dependencies

-   Update dependency com.google.cloud:google-iam-policy to v1.6.14 ([#&#8203;536](https://togithub.com/googleapis/java-iam/issues/536)) ([4e15368](https://togithub.com/googleapis/java-iam/commit/4e15368f6924253fe9e54d08ba7bd1b38b23b944))

</details>

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Author: renovate-bot

samples/cloud-client/snippets/pom.xml

@@ -41,7 +41,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-iam-policy</artifactId>
-      <version>1.6.14</version>
+      <version>1.6.15</version>
       <scope>compile</scope>
     </dependency>
     <dependency>