gh-104522: Change message returned by subprocess when cwd option is not the cause

[PurityLake]

Refers to #104522

Summary of change:
subprocess._execute_child would raise an exception referencing cwd as the cause of the issue even if this not the case.

So in the sample code:

import subprocess
subprocess.check_call(["pwd"], user="root", cwd="/tmp") 
# or
subprocess.check_call(["pwd"], pass_fds=[30,], cwd="/tmp")

subprocess will put the blame on cwd but raise the correct exception. This can be misleading to the user as to what the correct cause is.

Current state of this PR,:
The exception type is checked by instantiating an error object store in child_exception_type which is OSError, but when supplied the errno and any string can be tested with isinstance to check for FileNotFoundError and NotADirectoryError, these exceptions imply that cwd is most certainly the error as at this point as the subprocess was in preexec. Although if other errors are raise in this context the errno and message are still raised but contents of cwd will not be passed the exception.

• Issue: subprocess raises misleading exceptions from child failure pre-exec #104522

[serhiy-storchaka]

Good idea, but not very reliable. Other errno can be set by failing chdir(cwd) (such as EACCES or ELOOP), and we cannot guarantee that ENOENT and ENOTDIR can only be set by this call. I implemented more reliable way in #114195.

[gpshead]

thanks, Serhiy's other PR has been merged! :)