Fix T103589: right-clicking on the "Online Manual" button inside an "Online Manual" context menu created a duplicate "Online Manual" context menu. The same happened for the "Online Python Reference" context menu.
This PR fixes that by checking for if the currently opened context menu is that of "Online Manual". If it is, then
right-clicking the "Online Manual" button will no longer open the "Online Manual" context menu. Same
goes for the "Online Python Reference" context menu.
To know which type of context menu is currently opened, I didn't find any better way than to parse
the header label of the context menu. If a more experienced developer has a better alternative for
this, I'm happy to change it :).