fix: forum/discussion titles in notifications overflow

[dsevillamartin]

Fixes #3408

Changes proposed in this pull request:

• Apply overflow & ellipsis to span as well as parent element
  • The span appears when the title is a discussion title, as it separates discussion badges vs titles in the DOM

Reviewers should focus on:
Do we just want to wrap the forum title in a span?

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.