[Reg 5.9->5.10] QDockWidget gets unnecessarily resized when a QLabel inside the dock widget has its text changed

QDockWidget gets unnecessarily resized when a QLabel inside the dock widget has its text changed.

Step to reproduce:

Test sequence 1:

• run the sample attached
• stretch the dockwidgets using the mouse (see the image attached)
• press the button to trigger a change in the label (see the image attached)
  EXPECTED: the dock widgets keep their size when text is added to the label
  ACTUAL: the dock widgets are resized back to their original size when text is added to the label

Test sequence 2:

• run the sample attached
• detach either one of the dock widgets using the mouse
• place the dock widget back to its place
• stretch the dockwidgets using the mouse (see the image attached)
• press the button to trigger a change in the label (see the image attached)
  EXPECTED: the dock widgets keep their size when text is added to the label
  ACTUAL: the dock widgets DO keep their size when text is added to the label, so the buggy effect went away