Fix default client env when var is set (#2128)

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

tests/plan/client/env/default.cue

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"dagger.io/dagger"
+	"dagger.io/dagger/core"
+)
+
+dagger.#Plan & {
+	client: env: TEST_DEFAULT: string | *"hello world"
+	actions: {
+		image: core.#Pull & {
+			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
+		}
+		test: core.#Exec & {
+            input: image.output
+            args: ["test", client.env.TEST_DEFAULT, "=", "hello universe"]
+		}
+	}
+}