test(cypress): also run on stable27

Current development is diverging pretty quickly
in particular on the frontend side.

Make sure our tests still work on the latest stable release.

Signed-off-by: Max <max@nextcloud.com>

.github/workflows/cypress.yml

@@ -45,7 +45,7 @@ jobs:
 
     strategy:
       matrix:
-        server-versions: ['stable25', 'master']
+        server-versions: ['stable25', 'stable27', 'master']
 
     steps:
       - name: Checkout server