Update myst-parser requirement from <2.0,>=1.0 to >=1.0,<3.0

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...v2.0.0)

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

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

requirements/docs.txt

@@ -5,7 +5,7 @@ sphinx-autodoc-typehints>=1.12.0, <1.21  # limited due to https://github.com/tox
 sphinx-rtd-theme>=1.0.0, <2.0.0
 sphinxcontrib-apidoc>=0.3.0, <0.4.0
 sphinxcontrib-bibtex>=2.1.0, <3.0.0
-myst-parser>=1.0, <2.0
+myst-parser>=1.0, <3.0
 nbsphinx>=0.8.5, <0.10.0
 sphinx_design==0.4.1  # Pinning for now as sphinx_design is v.new and still in flux.
 ipykernel>=5.1.0, <7.0.0 # required for executing notebooks via nbsphinx