Difference between opposite- and same-charge pair correlations for \gc{} divided by $v_2$  as a function of centrality (left) and charged-particle density (right) compared to results from Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV . The Pb--Pb points are slightly shifted along the horizontal axis for better visibility in the left panel. Bars (boxes) denote statistical (systematic) uncertainties.