Bump pillow from 8.3.2 to 8.4.0

Bumps [pillow](https://github.com/python-pillow/Pillow) from 8.3.2 to 8.4.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@8.3.2...8.4.0)

---
updated-dependencies:
- dependency-name: pillow
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements_dev.txt

@@ -4,7 +4,7 @@
 #---------------------------------------------------------
 coveralls==3.2.0
 flake8==4.0.1
-pillow==8.3.2
+pillow==8.4.0
 pytest==6.2.5
 pytest-cache==1.0
 pytest-cov==3.0.0