Use gitea rootless image in e2e test

Gitea 1.21 refuses to run as root. The non-rootless image's
entrypoint switches to the git user, but kubectl exec still runs
as root, causing `gitea admin user create` to fail with:
  "Gitea is not supposed to be run as root"

Switch to gitea/gitea:1.21-rootless which runs as UID 1000,
and mount emptyDir volumes at /var/lib/gitea and /etc/gitea.

https://claude.ai/code/session_01QfFzqKQUsxxBsiZUhuJ3pG

.github/workflows/ci.yaml

@@ -111,7 +111,7 @@ jobs:
               spec:
                 containers:
                 - name: gitea
-                  image: gitea/gitea:1.21
+                  image: gitea/gitea:1.21-rootless
                   ports:
                   - containerPort: 3000
                     name: http
@@ -132,10 +132,14 @@ jobs:
                       memory: 256Mi
                   volumeMounts:
                   - name: data
-                    mountPath: /data
+                    mountPath: /var/lib/gitea
+                  - name: config
+                    mountPath: /etc/gitea
                 volumes:
                 - name: data
                   emptyDir: {}
+                - name: config
+                  emptyDir: {}
           EOF
           kubectl apply -f - <<'EOF'
           apiVersion: v1