Quote everything inside stdout/contents except regexp (#51956)

Signed-off-by: Carlos Rodríguez Hernández <carlosrh@vmware.com>

.vib/wordpress/goss/wordpress.yaml

@@ -6,7 +6,7 @@ command:
     exec: sed -nE "s/.wp_version\s*=\s*'([0-9\.]+)';/\1/p" /opt/bitnami/wordpress/wp-includes/version.php | sed -E 's/^[0-9]+\.[0-9]+$/&.0/'
     exit-status: 0
     stdout:
-      - {{ .Env.APP_VERSION }}
+      - "{{ .Env.APP_VERSION }}"
   # WP-CLI points to correct binaries and config file
   check-wp-cli-conf:
     exec: wp --info