Message when openning an branch for an issue should be improved

[guillep]

From https://github.com/pharo-project/pharo/issues/2965

The pic talks by itself

the "remote" field is a drop down (not visible). You need to select the pharo repository there. Yes, that needs to be simplified and improved.

[...]

What about using "INVALID-ISSUE-FOR-REMOTE" instead of "INVALID_ISSUE" so one could at least have an idea it might be due to the selected remote...