deps: update dependency com.google.errorprone:error_prone_annotations to v2.6.0 (#1327)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| com.google.errorprone:error_prone_annotations | `2.5.1` -> `2.6.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.errorprone:error_prone_annotations/2.6.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.errorprone:error_prone_annotations/2.6.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.errorprone:error_prone_annotations/2.6.0/compatibility-slim/2.5.1)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.errorprone:error_prone_annotations/2.6.0/confidence-slim/2.5.1)](https://docs.renovatebot.com/merge-confidence/) |

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pom.xml

@@ -129,7 +129,7 @@
       <dependency>
         <groupId>com.google.errorprone</groupId>
         <artifactId>error_prone_annotations</artifactId>
-        <version>2.5.1</version>
+        <version>2.6.0</version>
       </dependency>
       <dependency>
         <groupId>com.google.appengine</groupId>