Bump gitpython from 3.1.3 to 3.1.8 in /cvat/requirements (#2143)

Bumps [gitpython](https://github.com/gitpython-developers/GitPython) from 3.1.3 to 3.1.8.
- [Release notes](https://github.com/gitpython-developers/GitPython/releases)
- [Changelog](https://github.com/gitpython-developers/GitPython/blob/master/CHANGES)
- [Commits](https://github.com/gitpython-developers/GitPython/compare/3.1.3...3.1.8)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

cvat/requirements/base.txt

@@ -24,7 +24,7 @@ dj-pagination==2.5.0
 python-logstash==0.4.6
 django-revproxy==0.10.0
 rules==2.2
-GitPython==3.1.3
+GitPython==3.1.8
 coreapi==2.3.3
 django-filter==2.3.0
 Markdown==3.2.2