ci(desec): drop obsolete SKIP_DOMAIN_VALIDATION from the deSEC test step

The deSEC registration entry point now renders regardless of
SKIP_DOMAIN_VALIDATION (it was moved out of the skip-validation guard), and
the deSEC flow already sets the domain with validation skipped internally.
Remove the now-unnecessary SKIP_DOMAIN_VALIDATION=false override from the
deSEC Playwright steps in both workflows and update the stale spec comment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Simon L. <szaimen@e.mail.de>

.github/workflows/playwright-on-push.yml

@@ -135,8 +135,9 @@ jobs:
           echo $! > desec-mock.pid
           docker rm --force nextcloud-aio-{mastercontainer,apache,notify-push,nextcloud,redis,database,domaincheck,whiteboard,imaginary,talk,collabora,borgbackup,caddy,dnsmasq} || true
           docker volume rm nextcloud_aio_{mastercontainer,apache,database,database_dump,nextcloud,nextcloud_data,redis,backup_cache,elasticsearch} || true
-          # SKIP_DOMAIN_VALIDATION=false so the deSEC registration form is rendered; the deSEC
-          # flow sets the domain with validation skipped internally regardless of this.
+          # The deSEC registration entry point renders regardless of SKIP_DOMAIN_VALIDATION,
+          # and the deSEC flow sets the domain with validation skipped internally, so no
+          # SKIP_DOMAIN_VALIDATION override is needed here.
           docker run \
             -d \
             --init \
@@ -151,7 +152,6 @@ jobs:
             --volume ./Containers/mastercontainer/headers.Caddyfile:/headers.Caddyfile \
             --volume ./Containers/mastercontainer/start.sh:/start.sh \
             --volume /var/run/docker.sock:/var/run/docker.sock:ro \
-            --env SKIP_DOMAIN_VALIDATION=false \
             --env APACHE_PORT=11000 \
             ghcr.io/nextcloud-releases/all-in-one:develop
           echo Waiting for 10 seconds for the development container to start ...