Run and advance command caption doesn't adapt when selecting more than one cell

[HaudinFlorence]

Description

In a recent PR #13861, some changes were proposed to adapt the caption associated to the different buttons of the notebook toolbar. Most particularly, when selecting more than one cell, the number of cells is changing in the displayed caption, as shown here (in the case of copy cells command) :

Nevertheless, it appears that the caption doesn't adapt for the run and advance command as shown here:

Reproduce

1. Open a notebook
2. Click on the run and advance button (play triangular button) and check the caption: it is "Run this cell and advance"
3. Add n cells and select the n+1 cells of the notebook
4. Click again on the run and advance button
5. See the corresponding caption: it still mentions a single cell

Expected behavior

When n cells are selected, the caption should be "Run these n cells and advance"