make TestService_UserReplies more robust

It flaps (see #380), and with this change it will
have more time to get the expected output in flaky
GitHub Actions environment.

backend/app/store/service/service_test.go

@@ -1057,10 +1057,12 @@ func TestService_UserReplies(t *testing.T) {
 	require.Equal(t, 3, len(cc), "3 replies to u1")
 	assert.Equal(t, "developer one u1", u)
 
-	cc, u, err = b.UserReplies("radio-t", "u1", 10, time.Millisecond*199)
-	assert.NoError(t, err)
-	require.Equal(t, 1, len(cc), "1 reply to u1 in last 200ms")
-	assert.Equal(t, "developer one u1", u)
+	assert.Eventuallyf(t, func() bool {
+		cc, u, err = b.UserReplies("radio-t", "u1", 10, time.Millisecond*199)
+		require.NoError(t, err)
+		require.Equal(t, "developer one u1", u)
+		return len(cc) == 1
+	}, time.Second, 100*time.Millisecond, "1 reply to u1")
 
 	cc, u, err = b.UserReplies("radio-t", "u2", 10, time.Hour)
 	assert.NoError(t, err)