Conflicting {change, commit}.shortest() and bookmark or tag name

[avamsi]

Description

I have a change for which jj reports the shortest change ID is l, but turns out there's an (old) branch in the repo named l (which jj resolves to, when asked for l), but I would probably expect for jj to resolve to both (out of caution) or maybe consider branches (and other references) when reporting shortest, so this is not an issue in the first place.

Steps to Reproduce the Problem

Pick {change, commit}.shortest() from a random commit and create a new branch with the same name on another commit.

[necauqua]

Actually, yeah, that bit me in the past.
The shortest unique changeid/commitid prefix that matches a branch/tag shouldn't exist - it should be 1 longer [repeat until actually unique]