Fix mypy configuration by ignoring two files, to satisfy CI

[amotl]

Hi again,

at GH-1709, we discovered that the test suite on CI currently croaks from an error with mypy. mypy raised this error on four occasions (see below):

error: "_SupportsAcloseT" has no attribute "__aiter__" (not async iterable)  [attr-defined]

This patch aims to silence this error by ignoring the corresponding files, in order to satisfy CI. Let us know if you think this should be made happen differently.

With kind regards,
Andreas.

---

The root cause are those errors, where both python/mypy#10301 and python/mypy#5385 (comment) have interesting information, with a specific suggestion by @JelleZijlstra:

I think you shouldn't make the protocol function async def, but just def. Conceptually, an async generator is a callable that returns an AsyncIterator (or more precisely, an AsyncGenerator). But an async def function without a yield returns an Awaitable of whatever its declared return type is, so that's how mypy interprets your protocol.

$ mypy --strict src/prompt_toolkit --platform win32
src/prompt_toolkit/completion/base.py:284: error: "_SupportsAcloseT" has no attribute "__aiter__" (not async iterable)  [attr-defined]
src/prompt_toolkit/completion/base.py:367: error: "_SupportsAcloseT" has no attribute "__aiter__" (not async iterable)  [attr-defined]
src/prompt_toolkit/completion/base.py:395: error: "_SupportsAcloseT" has no attribute "__aiter__" (not async iterable)  [attr-defined]
src/prompt_toolkit/buffer.py:1763: error: "_SupportsAcloseT" has no attribute "__aiter__" (not async iterable)  [attr-defined]

[jonathanslenders]

Hi @amotl! Thanks for pointing out the issue.

I just had a look. No need to ignore anything.
This should fix it instead: #1711

[amotl]

Lovely. Thanks for fixing it in a correct way so quickly.