build(deps): update myst-parser requirement from <4.0.0,>=0.18.1 to >=0.18.1,<5.0.0 in /requirements (#21114)

build(deps): update myst-parser requirement in /requirements

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@v0.18.1...v4.0.1)

---
updated-dependencies:
- dependency-name: myst-parser
  dependency-version: 4.0.1
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
(cherry picked from commit 91ec79f)

Author: dependabot[bot]

requirements/docs.txt

@@ -1,5 +1,5 @@
 sphinx >5.0, <6.0
-myst-parser >=0.18.1, <4.0.0
+myst-parser >=0.18.1, <5.0.0
 nbsphinx >=0.8.5, <=0.9.7
 nbconvert >7.14, <7.17
 pandoc >=1.0, <=2.4