Fix the `slug` function to remove *all* emojis in the Supplemental
Symbols and Pictographs Unicode block.
I'm not sure why originally only a partial range was removed, but this
change seems to align with GitHub-flavored Markdown.
While this will effectively fix issue #5998, it does not address the
underlying problem where slugs were never designed for widget IDs.
* Update snapshots
* Update to use textual-snapshot v1.0.0
* Dont use xdist on CI
* Update pytest-cov to fix warnings
* Remove xdist thing from pythonpackage.yml GitHub workflow
This isn't 100% how GitHub's approach works, but the edge cases I can find
appear to be bugs or issues with how GitHub handle the more interesting
emoji when they appear in headers.
Long story short: they appear to just strip emoji for the most part, but if
an emoji is modified in some interesting way (think shrugging person vs
shrugging light-skinned woman with black hair) it looks like the final
codepoint "leaks" into the slug; nothing about this looks intentional, and
it's such a remote issue that it's hardly worth supporting.
