Update myst-parser requirement from <3.0,>=1.0 to >=1.0,<5.0

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@v1.0.0...v4.0.0)

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

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

Author: dependabot[bot]

requirements/docs.txt

@@ -3,7 +3,7 @@
 sphinx>=4.2.0, <8.2.0
 sphinx-autodoc-typehints>=1.12.0, <2.6.0
 sphinx-rtd-theme>=1.0.0, <3.1.0
-myst-parser>=1.0, <3.0
+myst-parser>=1.0, <5.0
 sphinxcontrib-apidoc>=0.3.0, <0.6.0
 nbsphinx>=0.8.5, <0.10.0
 sphinx_design==0.6.1  # Pinning for now as sphinx_design is v.new and still in flux.