fix(deps): update dependency checkstyle to v10.21.0 (#6951)

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

buildSrc/src/main/kotlin/otel.java-conventions.gradle.kts

@@ -42,7 +42,7 @@ java {
 
 checkstyle {
   configDirectory.set(file("$rootDir/buildscripts/"))
-  toolVersion = "10.20.2"
+  toolVersion = "10.21.0"
   isIgnoreFailures = false
   configProperties["rootDir"] = rootDir
 }