Bump imageio-ffmpeg from 0.5.1 to 0.6.0 (#788)

Bumps [imageio-ffmpeg](https://github.com/imageio/imageio-ffmpeg) from 0.5.1 to 0.6.0.
- [Release notes](https://github.com/imageio/imageio-ffmpeg/releases)
- [Commits](imageio/imageio-ffmpeg@v0.5.1...v0.6.0)

---
updated-dependencies:
- dependency-name: imageio-ffmpeg
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements/requirements_docs.txt

@@ -1,7 +1,7 @@
 pypandoc==1.15
 imageio==2.36.1
 numpydoc==1.8.0
-imageio-ffmpeg==0.5.1
+imageio-ffmpeg==0.6.0
 Sphinx==8.1.3
 sphinxcontrib-napoleon==0.7
 sphinxcontrib-websupport==2.0.0