Bump myst-nb from 1.2.0 to 1.3.0 (#821)

Bumps [myst-nb](https://github.com/executablebooks/myst-nb) from 1.2.0 to 1.3.0.
- [Release notes](https://github.com/executablebooks/myst-nb/releases)
- [Changelog](https://github.com/executablebooks/MyST-NB/blob/main/CHANGELOG.md)
- [Commits](executablebooks/MyST-NB@v1.2.0...v1.3.0)

---
updated-dependencies:
- dependency-name: myst-nb
  dependency-version: 1.3.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,6 +1,6 @@
 sphinx==8.2.3
 pangeo-sphinx-book-theme==0.2
-myst-nb==1.2.0
+myst-nb==1.3.0
 sphinx-copybutton==0.5.2
 sphinx-togglebutton==0.3.2
 sphinx-autodoc-typehints==3.2.0