Cirrus CI: fixup the previous commit

Error while parsing tasks: INVALID_ARGUMENT: yaml: line 30: did not find
expected alphabetic or numeric character!

.cirrus.yml

@@ -27,7 +27,7 @@ task:
   script:
     - apt-get -qqy update
     - apt-get -qqy install mariadb-server make curl php-cli php-xml php-gd php-mysql php-mbstring php-bcmath php-json >/dev/null
-    - [ "$INSTALL_SHELLCHECK" = yes ] && apt-get -qqy install shellcheck >/dev/null
+    - test "$INSTALL_SHELLCHECK" = yes && apt-get -qqy install shellcheck >/dev/null
     # MariaDB has no systemd props in Ubuntu 16.04, rc.d props work even in
     # Ubuntu 20.04.
     - test -S /var/run/mysqld/mysqld.sock && service mysql stop