tests: ops: use proper imports

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

tests/ops/exec/env/invalid/main.cue

@@ -1,12 +1,12 @@
 package testing
 
+import "dagger.io/dagger/op"
+
 #up: [
-	{
-		do:  "fetch-container"
+	op.#FetchContainer & {
 		ref: "alpine"
 	},
-	{
-		do: "exec"
+	op.#Exec & {
 		args: ["sh", "-c", #"""
 			echo "$foo"
 			"""#]