CI: Upload failed screendump tests when run in github actions

CI: Upload failed screendump tests when run in github actions

It's a bit of a pain to debug failing screendump tests without knowing
exactly what went wrong. Therefore include actions/upload-artifact for
the Github CI runners and have them uploaded those failing screen dump
tests automatically.

Let's add this step to each of the Linux/MacOS/Windows workflows but do
not duplicate the code, factor it out to a single file
.github/actions/screendump/action.yml and reference this one from the
main ci.yml file

Example:
https://github.com/chrisbra/vim/actions/runs/9085493619

closes: #14771

Co-authored-by: dundargoc <gocdundar@gmail.com>
Co-authored-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>