Wait longer in timing sensitive test

Less likely to fail on CI.

pgxpool/pool_test.go

@@ -278,7 +278,7 @@ func TestPoolBackgroundChecksMaxConnLifetime(t *testing.T) {
 	c, err := db.Acquire(context.Background())
 	require.NoError(t, err)
 	c.Release()
-	time.Sleep(config.MaxConnLifetime + 50*time.Millisecond)
+	time.Sleep(config.MaxConnLifetime + 100*time.Millisecond)
 
 	stats := db.Stat()
 	assert.EqualValues(t, 0, stats.TotalConns())