Bump myst-parser from 0.17.2 to 0.18.1 in /docs

Bumps [myst-parser](https://github.com/executablebooks/MyST-Parser) from 0.17.2 to 0.18.1.
- [Release notes](https://github.com/executablebooks/MyST-Parser/releases)
- [Changelog](https://github.com/executablebooks/MyST-Parser/blob/master/CHANGELOG.md)
- [Commits](executablebooks/MyST-Parser@v0.17.2...v0.18.1)

---
updated-dependencies:
- dependency-name: myst-parser
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,4 +1,4 @@
 furo==2022.4.7
 sphinx==4.5.0
 sphinx-click==4.1.0
-myst_parser==0.17.2
+myst_parser==0.18.1