Chore(deps): Update myst-parser[linkify] requirement

Updates the requirements on [myst-parser[linkify]](https://github.com/executablebooks/MyST-Parser) to permit the latest version.
- [Release notes](https://github.com/executablebooks/MyST-Parser/releases)
- [Changelog](https://github.com/executablebooks/MyST-Parser/blob/master/CHANGELOG.md)
- [Commits](executablebooks/MyST-Parser@v0.18.0...v4.0.0)

---
updated-dependencies:
- dependency-name: myst-parser[linkify]
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

pyproject.toml

@@ -122,7 +122,7 @@ optional-dependencies.develop = [
 ]
 optional-dependencies.doc = [
   "furo==2024.1.29",               # Check visited link style on newer versions!
-  "myst-parser[linkify]>=0.18,<4",
+  "myst-parser[linkify]>=0.18,<5",
   "sphinx-autobuild==2021.3.14",   # Newer versions stopped "watching" appropriately?
   "sphinx-copybutton",
   "sphinx-design-elements<1",