Update myst-parser requirement from <2.1.0 to <3.1.0

Updates the requirements on [myst-parser](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@v0.3.0...v3.0.1)

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

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

docs/sphinx-requirements.txt

@@ -10,4 +10,4 @@ sphinx-automodapi
 sphinx-gallery
 
 # Markdown conversion
-myst-parser<2.1.0
+myst-parser<3.1.0