ci: detect command not found build errors

tools/ci/build_examples.sh

@@ -152,7 +152,7 @@ build_example () {
         cat ${BUILDLOG}
     popd
 
-    grep -i "error\|warning" "${BUILDLOG}" 2>&1 >> "${LOG_SUSPECTED}" || :
+    grep -i "error\|warning\|command not found" "${BUILDLOG}" 2>&1 >> "${LOG_SUSPECTED}" || :
 }
 
 EXAMPLE_NUM=0