chore: add debug output to build.sh for missing modules

Author: lqiu96

.kokoro/build.sh

@@ -233,6 +233,7 @@ case ${JOB_TYPE} in
                 if [ -f "${dir}/pom.xml" ] && [ "${dir}" != "." ]; then
                     # Exclude sample modules as they are not in the default reactor
                     if [[ "${dir}" != *"samples"* ]]; then
+                        echo "Processed file: ${changed_file} -> resolved module: ${dir}"
                         changed_modules+=("${dir}")
                     fi
                 fi