Build(deps-dev): Bump mypy from 0.812 to 0.902 (#390)

* Build(deps-dev): Bump mypy from 0.812 to 0.902

Bumps [mypy](https://github.com/python/mypy) from 0.812 to 0.902.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.812...v0.902)

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

Signed-off-by: dependabot[bot] <[email protected]>

* ci: Install types-dataclasses in mypy session for Python 3.6

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Claudio Jolowicz <[email protected]>

noxfile.py

@@ -109,8 +109,10 @@ def safety(session: Session) -> None:
 def mypy(session: Session) -> None:
     """Type-check using mypy."""
     args = session.posargs or ["src", "tests", "docs/conf.py"]
-    session.install(".")
-    session.install("mypy", "pytest")
+    deps = [".", "mypy", "pytest"] + (
+        ["types-dataclasses"] if session.python == "3.6" else []
+    )
+    session.install(*deps)
     session.run("mypy", *args)
     if not session.posargs:
         session.run("mypy", f"--python-executable={sys.executable}", "noxfile.py")