mypy: Use ‘strict’ option to enable (almost) all strictness flags.
mypy: Use ‘strict’ option to enable (almost) all strictness flags.

The ‘strict’ configuration option has been supported since mypy 0.770,
and I added it to their documentation in 0.920.

https://mypy.readthedocs.io/en/stable/config_file.html#confval-strict

This has the effect of enabling the new ‘strict_concatenate’ option
from 0.950.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

rht/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip