MR diff/changes version bar doesn't reach 100% width, while content does

problem

MR diff/changes version bar doesn't reach 100% width, while content does

this results in weird looking UI.

Proposal

cc: @iamphill because this touches some places you have touched with the new width for texts :) cc: @annabeldunstone (i believe i saw you comment there)

changed milestone to %Next 2-3 months in gitlab-foss

added Discussion in GitLab FOSS label

moved from gitlab-foss#34260 (moved)