doc: Add mypy to test dependencies

Author: hebasto

test/README.md

@@ -261,6 +261,7 @@ Use the `-v` option for verbose output.
 | Lint test | Dependency | Version [used by CI](../ci/lint/04_install.sh) | Installation
 |-----------|:----------:|:-------------------------------------------:|--------------
 | [`lint-python.sh`](lint/lint-python.sh) | [flake8](https://gitlab.com/pycqa/flake8) | [3.7.8](https://github.com/bitcoin/bitcoin/pull/15257) | `pip3 install flake8==3.7.8`
+| [`lint-python.sh`](lint/lint-python.sh) | [mypy](https://github.com/python/mypy) | [0.700](https://github.com/bitcoin/bitcoin/pull/18210) | `pip3 install mypy==0.700`
 | [`lint-shell.sh`](lint/lint-shell.sh) | [ShellCheck](https://github.com/koalaman/shellcheck) | [0.6.0](https://github.com/bitcoin/bitcoin/pull/15166) | [details...](https://github.com/koalaman/shellcheck#installing)
 | [`lint-shell.sh`](lint/lint-shell.sh) | [yq](https://github.com/kislyuk/yq) | default | `pip3 install yq`
 | [`lint-spelling.sh`](lint/lint-spelling.sh) | [codespell](https://github.com/codespell-project/codespell) | [1.15.0](https://github.com/bitcoin/bitcoin/pull/16186) | `pip3 install codespell==1.15.0`