Presence of directories in `~/.ssh/config.d/` breaks parser

[jacopo-exact]

We use Include config.d/* in our ~/.ssh/config and use git to sync config.d content across our servers. Git creates its .git directory inside ~/.ssh/config.d/, which breaks the config parser with the following traceback.

Albeit one could argue that a more specific glob pattern should be used in the Include statement, ssh ignores directories in its own parsing, and so probably asyncssh should conform.

IsADirectoryError: [Errno 21] Is a directory: '/home/alberto/.ssh/config.d/.git'
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/misc.py", line 386 in __aenter__
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/connection.py", line 9184 in connect
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/connection.py", line 7317 in construct
File "[REDACTED]/.venv/lib/python3.12/site-packages/greenback/_impl.py", line 210 in _greenback_shim
File "[REDACTED]/.local/share/uv/python/cpython-3.12.11-linux-x86_64-gnu/lib/python3.12/concurrent/futures/thread.py", line 59 in run
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/connection.py", line 7308 in __init__
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/misc.py", line 478 in __init__
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/connection.py", line 8146 in prepare
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/config.py", line 464 in load
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/config.py", line 424 in parse
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/config.py", line 155 in _include
File "[REDACTED]/.venv/lib/python3.12/site-packages/asyncssh/config.py", line 373 in parse

Will open a PR shortly. Thanks for the project.
cc @apasto

[ronf]

PR #785 is now merged into the develop branch and will be included in the next release. Thanks for your contribution, @jacopo-exact!

See also commit c7bc3aa which adds a unit test for this case.