Bump imageio from 2.28.0 to 2.31.3 in /requirements

Bumps [imageio](https://github.com/imageio/imageio) from 2.28.0 to 2.31.3.
- [Release notes](https://github.com/imageio/imageio/releases)
- [Changelog](https://github.com/imageio/imageio/blob/master/CHANGELOG.md)
- [Commits](imageio/imageio@v2.28.0...v2.31.3)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/requirements_docs.txt

@@ -1,7 +1,7 @@
 ansys_sphinx_theme==0.11.1
 enum-tools[sphinx]==0.9.0.post1
 graphviz==0.20.1
-imageio==2.28.0
+imageio==2.31.3
 imageio-ffmpeg==0.4.7
 nbsphinx==0.9.1
 pypandoc==1.11

requirements/requirements_test.txt

@@ -1,6 +1,6 @@
 ansys-platform-instancemanagement==1.1.1
 coverage==7.2.7
-imageio==2.28.0
+imageio==2.31.3
 imageio-ffmpeg==0.4.7
 pytest==7.2.0
 pytest-cov==4.1.0