auto updates: stop running update tests if received null value from api (#7619)

When this happens, it's time to update github-projects.txt.

scripts/updates/check-updates.sh

@@ -49,7 +49,7 @@ if [ -f "${BASEDIR}/github-projects.txt" ]; then
 			latest_version=$(grep -oP "$version_regexp" <<< "$latest_version" || true)
 		fi
 
-		if [ -z "$latest_version" ]; then
+		if [[ -z "$latest_version" || "$latest_version" = "null" ]]; then
 			echo "Failed to get latest version for '${package}'. Update 'github-projects.txt'."
 			exit 1
 		fi