Bump django from 2.2.18 to 2.2.20 in /perf_dashboard (#1495)
Bump django from 2.2.18 to 2.2.20 in /perf_dashboard (#1495)

Bumps [django](https://github.com/django/django) from 2.2.18 to 2.2.20.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.2.18...2.2.20)

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Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
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