fix(deps): update dependency checkstyle to v10.21.0 (#12885)

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

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

@@ -430,7 +430,7 @@ codenarc {
 checkstyle {
   configFile = rootProject.file("buildscripts/checkstyle.xml")
   // this version should match the version of google_checks.xml used as basis for above configuration
-  toolVersion = "10.20.2"
+  toolVersion = "10.21.0"
   maxWarnings = 0
 }