⬆ Update mypy requirement from 0.930 to 0.971 (#380)

Update mypy requirement from 0.930 to 0.971

Updates the requirements on [mypy](https://github.com/python/mypy) to permit the latest version.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.930...v0.971)

---
updated-dependencies:
- dependency-name: mypy
  dependency-type: direct:development
...

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pyproject.toml

@@ -37,7 +37,7 @@ sqlalchemy2-stubs = {version = "*", allow-prereleases = true}
 
 [tool.poetry.dev-dependencies]
 pytest = "^7.0.1"
-mypy = "0.930"
+mypy = "0.971"
 flake8 = "^5.0.4"
 black = {version = "^21.5-beta.1", python = "^3.7"}
 mkdocs = "^1.2.1"