build(deps): bump pyvista from 0.43.7 to 0.43.8 in /requirements (#426)

Bumps [pyvista](https://github.com/pyvista/pyvista) from 0.43.7 to 0.43.8.
- [Release notes](https://github.com/pyvista/pyvista/releases)
- [Commits](pyvista/pyvista@v0.43.7...v0.43.8)

---
updated-dependencies:
- dependency-name: pyvista
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

requirements/requirements_doc.txt

@@ -4,7 +4,7 @@ imageio==2.34.1
 nest-asyncio==1.6.0
 notfound==1.0.2
 pypandoc==1.13
-pyvista==0.43.7
+pyvista==0.43.8
 sphinx-copybutton==0.5.2
 sphinx-gallery==0.16.0
 sphinx-notfound-page==1.0.0