mypy(shell): Allow untyped calls

I do not think this handled the solution surgically, it seems to force losing
safety for the rule across a *whole file* rather than surgically at the offending
line.

See also: python/mypy#12076, python/mypy#13512

src/tmuxp/shell.py

@@ -1,3 +1,4 @@
+# mypy: allow-untyped-calls
 """Utility and helper methods for tmuxp."""
 
 import logging