chore(deps): Update error-prone monorepo to v2.21.1 (#9)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

gradle/libs.versions.toml

@@ -2,7 +2,7 @@
 version = "1.0"
 
 [versions]
-errorprone = "2.18.0"
+errorprone = "2.21.1"
 errorproneGradle = "3.1.0"
 junit = "5.10.0"
 indra = "3.1.3"