Update myst-parser requirement from ==0.15.* to ==0.16.*

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](https://github.com/executablebooks/MyST-Parser/compare/v0.15.0...v0.16.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/requirements.txt b/requirements.txt
index 6edc5e1..12f20c4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,7 +3,7 @@
 docutils == 0.17.*
 cython == 0.*
 more_itertools == 8.*
-myst-parser == 0.15.*
+myst-parser == 0.16.*
 sphinx == 4.*
 sphinx_autodoc_typehints == 1.*
 sphinx_rtd_theme == 1.*