spindle/engine: fix flaky envs test

Signed-off-by: Anirudh Oppiliappan <[e-mail]>

spindle/engine/envs_test.go

···
 	ev.AddEnv("FOO", "bar")
 	ev.AddEnv("BAZ", "qux")
 	want := EnvVars{"FOO=bar", "BAZ=qux"}
-	assert.Equal(t, want, ev)
+	assert.ElementsMatch(t, want, ev)
 }