Update myst-parser requirement from <0.18.0,>=0.15.2 to >=0.15.2,<2.1.0

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@v0.15.2...v2.0.0)

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

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

dev-requirements.txt

@@ -27,7 +27,7 @@ Sphinx>=4.3.0,<5.1.0
 furo==2022.4.7
 
 # Lets Sphinx parse markdown files in addition to rst.
-myst-parser>=0.15.2,<0.18.0
+myst-parser>=0.15.2,<2.1.0
 
 # Adds a copy button to code examples in the docs.
 sphinx-copybutton==0.5.0