fix(relay): keep local E2E tests independent of production upstream (#8514)

Wrangler local mode retains deployment vars, so relay readiness probes were forwarded to an unavailable upstream instead of the local Durable Object. Clear that binding only in the E2E launcher.

Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>
(cherry picked from commit b280ca5355)

packages/relay/src/e2e.test.ts

@@ -56,6 +56,9 @@ function spawnRelayDevServer(port: number): ChildProcess {
       wranglerCliPath,
       "dev",
       "--local",
+      // Local execution still inherits production vars; exercise the local Durable Object.
+      "--var",
+      "PASEO_RELAY_UPSTREAM:",
       "--ip",
       "127.0.0.1",
       "--port",