Dependency(deps): Bump com.google.errorprone:error_prone_core

Bumps [com.google.errorprone:error_prone_core](https://github.com/google/error-prone) from 2.21.0 to 2.21.1.
- [Release notes](https://github.com/google/error-prone/releases)
- [Commits](google/error-prone@v2.21.0...v2.21.1)

---
updated-dependencies:
- dependency-name: com.google.errorprone:error_prone_core
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

autograder-core/pom.xml

@@ -113,7 +113,7 @@
         <dependency>
             <groupId>com.google.errorprone</groupId>
             <artifactId>error_prone_core</artifactId>
-            <version>2.21.0</version>
+            <version>2.21.1</version>
         </dependency>
 
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