Bump pyupgrade from 2.7.2 to 2.7.3

Bumps [pyupgrade](https://github.com/asottile/pyupgrade) from 2.7.2 to 2.7.3.
- [Release notes](https://github.com/asottile/pyupgrade/releases)
- [Commits](asottile/pyupgrade@v2.7.2...v2.7.3)

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

Author: dependabot[bot]

requirements-dev.txt

@@ -6,5 +6,5 @@ flake8-docstrings==1.5.0
 flake8==3.8.4
 isort==5.6.4
 pydocstyle==5.1.1
-pyupgrade==2.7.2
+pyupgrade==2.7.3
 pre-commit>=2.4.0