Set show_error_codes = True in mypy-strict.ini (#56616)
Summary:
This should make it easier to resolve issues surfaced by https://github.com/pytorch/pytorch/issues/56290. Also see https://github.com/pytorch/pytorch/pull/56559#discussion_r617828152 for context.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56616
Test Plan:
You could add a type error in a strict-checked file like `tools/test_history.py`, and then run this command:
```
$ mypy --config=mypy-strict.ini tools/test_history.py
```
Output before this PR:
```
tools/test_history.py:13:1: error: Function is missing a type annotation for one or more arguments
Found 1 error in 1 file (checked 1 source file)
```
Output after this PR:
```
tools/test_history.py:13:1: error: Function is missing a type annotation for one or more arguments [no-untyped-def]
Found 1 error in 1 file (checked 1 source file)
```
Reviewed By: driazati
Differential Revision: D27918753
Pulled By: samestep
fbshipit-source-id: 953926e019a7669da9004fd54498b414aec777a6
