fix(coderd/aibridged): retain dialer notification (#27529)

Fixes flake caused by race in `TestReady/FalseBeforeConnection` test.

coderd/aibridged/aibridged_test.go

@@ -1007,7 +1007,7 @@ func TestReady(t *testing.T) {
 		pool := mock.NewMockPooler(ctrl)
 		pool.EXPECT().Shutdown(gomock.Any()).MinTimes(1).Return(nil)
 
-		dialerCalled := make(chan struct{})
+		dialerCalled := make(chan struct{}, 1)
 		blockDialer := func(ctx context.Context) (aibridged.DRPCClient, error) {
 			select {
 			case dialerCalled <- struct{}{}: