Revert back to errorProne=true now that the JDK to use has been downgraded from 24.0 to 1.8

Author: kannanjgithub

buildscripts/kokoro/unix.sh

@@ -46,7 +46,7 @@ if [[ "$(uname -s)" == "Darwin" ]]; then
 fi
 GRADLE_FLAGS+=" -Pcheckstyle.ignoreFailures=false"
 GRADLE_FLAGS+=" -PfailOnWarnings=true"
-GRADLE_FLAGS+=" -PerrorProne=false"
+GRADLE_FLAGS+=" -PerrorProne=true"
 GRADLE_FLAGS+=" -Dorg.gradle.parallel=true"
 if [[ -z "${ALL_ARTIFACTS:-}" ]]; then
   GRADLE_FLAGS+=" -PskipAndroid=true"