stats: replace Copy with ShallowCopy for table stats update logic (#62430)

ref pingcap/tidb#57868

pkg/statistics/handle/cache/statscache.go

@@ -206,7 +206,7 @@ func (s *StatsCacheImpl) Update(ctx context.Context, is infoschema.InfoSchema, t
 		// If the column/index stats has not been updated, we can reuse the old table stats.
 		// Only need to update the count and modify count.
 		if ok && latestHistUpdateVersion > 0 && oldTbl.LastStatsHistVersion >= latestHistUpdateVersion {
-			tbl = oldTbl.Copy()
+			tbl = oldTbl.ShallowCopy()
 			// count and modify count is updated in finalProcess
 			needLoadColAndIdxStats = false
 		}

pkg/statistics/handle/handletest/handle_test.go

@@ -249,7 +249,7 @@ func TestLoadHist(t *testing.T) {
 	require.False(t, newStatsTbl2 == newStatsTbl)
 	// The histograms is not updated.
 	newStatsTbl.ForEachColumnImmutable(func(id int64, hist *statistics.Column) bool {
-		require.Equal(t, newStatsTbl2.GetCol(id), hist)
+		require.Equal(t, hist.LastUpdateVersion, newStatsTbl2.GetCol(id).LastUpdateVersion)
 		return false
 	})
 	require.Greater(t, newStatsTbl2.GetCol(3).LastUpdateVersion, newStatsTbl2.GetCol(1).LastUpdateVersion)