test: fix $namespace binding scope in TPP Enforce e2e

The hostname binding referenced $namespace at spec level, where it is not
yet defined, so chainsaw aborted the test with "variable not defined:
$namespace" before any step ran. Move the binding into the two steps that
use it, where the per-test namespace is in scope.

Verified against the fixed operator image on the local WAF stack: the test
now runs and passes (benign GET returns the backend's 200).

Author: ecv

test/e2e/trafficprotectionpolicy-enforce/chainsaw-test.yaml

@@ -22,9 +22,6 @@ spec:
     metadata:
       labels:
         meta.datumapis.com/upstream-cluster-name: e2e
-  bindings:
-    - name: hostname
-      value: (join('.', [$namespace, 'e2e.test']))
   steps:
     - name: Deploy a backend
       try:
@@ -72,6 +69,9 @@ spec:
                 availableReplicas: 1
 
     - name: Route through the WAF gateway with an Enforce policy
+      bindings:
+        - name: hostname
+          value: (join('.', [$namespace, 'e2e.test']))
       try:
         - apply:
             resource:
@@ -141,6 +141,9 @@ spec:
         not sufficient on its own — EG reports Programmed from its own
         translation, independent of Envoy's xDS ACK — so this asserts on the
         wire.
+      bindings:
+        - name: hostname
+          value: (join('.', [$namespace, 'e2e.test']))
       try:
         - script:
             env: