fix(test): screen:expect() render crash masks the real failure #40593

Problem:
When screen:expect() fails, it renders a snapshot for the error
message. If the grid references a highlight id that was never defined
via "hl_attr_define", the renderer crashes:

    screen.lua:1910: attempt to index local 'entry' (a nil value)

This hides the actual failure, and appears "flaky": it only fires on the
failure path, and only when the shared screen is missing an id the grid
still references. A screen created in setup() attaches mid-session, so
highlight ids allocated before it attached (still referenced by stale
grid cells) are never sent to it.

Solution:
- Don't crash while rendering a diagnostic: show undefined highlight ids
  as "UNKNOWN_HL_ID(n)", so the real failure and the desync are legible.
- put_spec: fix `visualbell` typo. If it fails again then we can find
  the actual root cause.

ref https://github.com/neovim/neovim/issues/36250

0 files changed, 0 insertions, 0 deletions