deps: update dependency com.google.cloud:google-cloud-core to v2.8.8 (#913)

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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) | `2.8.7` -> `2.8.8` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.8/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.8/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.8/compatibility-slim/2.8.7)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.8/confidence-slim/2.8.7)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v2.8.8`](https://togithub.com/googleapis/java-core/blob/HEAD/CHANGELOG.md#&#8203;288-httpsgithubcomgoogleapisjava-corecomparev287v288-2022-08-04)

[Compare Source](https://togithub.com/googleapis/java-core/compare/v2.8.7...v2.8.8)

##### Dependencies

-   update dependency com.google.errorprone:error_prone_annotations to v2.15.0 ([#&#8203;897](https://togithub.com/googleapis/java-core/issues/897)) ([29e4fc9](https://togithub.com/googleapis/java-core/commit/29e4fc93d5d4d50f7de85eae7a8150314cca6f43))

</details>

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Author: renovate-bot

samples/install-without-bom/pom.xml

@@ -36,7 +36,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.8.7</version>
+      <version>2.8.8</version>
     </dependency>
     <dependency>
       <groupId>junit</groupId>

samples/snapshot/pom.xml

@@ -35,7 +35,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.8.7</version>
+      <version>2.8.8</version>
     </dependency>
     <dependency>
       <groupId>junit</groupId>