Update myst-parser[linkify] requirement in /requirements

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@v1.0.0...v4.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/documentation.txt

@@ -1,7 +1,7 @@
 # Documentation (for devs)
 # -----------------------
 
-myst-parser[linkify]>=1,<3.1
+myst-parser[linkify]>=1,<4.1
 sphinx-autobuild==2024.*
 sphinx-copybutton>=0.2,<1
 sphinx-rtd-theme>=1,<3