Fix syntax error

Author: vmcj

.github/jobs/unit-tests.sh

@@ -25,7 +25,7 @@ cp webapp/.env.test /opt/domjudge/domserver/webapp/
 # We also need the composer.json for PHPunit to detect the correct directory.
 cp webapp/composer.json /opt/domjudge/domserver/webapp/
 
-cd /opt/domjudge/domserver
+cd /opt/domjudge/domserver || exit 1
 
 # Run phpunit tests.
 pcov=""