tsnet: use tstest.Shard in new tsnet tests

This helps us distribute tests across CI runners. Most tsnet tests call
tstest.Shard, but two recently added tests do not: tsnet.TestFunnelClose
and tsnet.TestListenService. This commit resolves the oversight.

Fixes tailscale/corp#36242

Signed-off-by: Harry Harpham <harry@tailscale.com>

tsnet/tsnet_test.go

@@ -846,6 +846,8 @@ func TestFunnel(t *testing.T) {
 // after itself when closed. Specifically, changes made to the serve config
 // should be cleared.
 func TestFunnelClose(t *testing.T) {
+	tstest.Shard(t)
+
 	marshalServeConfig := func(t *testing.T, sc ipn.ServeConfigView) string {
 		t.Helper()
 		return string(must.Get(json.MarshalIndent(sc, "", "\t")))
@@ -942,6 +944,8 @@ func TestFunnelClose(t *testing.T) {
 }
 
 func TestListenService(t *testing.T) {
+	tstest.Shard(t)
+
 	// First test an error case which doesn't require all of the fancy setup.
 	t.Run("untagged_node_error", func(t *testing.T) {
 		ctx := t.Context()