Use Path objects within copyfile

[AA-Turner]

#12690 (comment)

A

[jfbu]

Yes it fixes the output at my locale reported at comment.

(I do get unrelated C domain warnings I have been seeing for long time and not paying much attention to as they seem innocuous

/.../sphinx/doc/usage/domains/c.rst:228: WARNING: Duplicate C declaration, also defined at usage/domains/c:228.
Declaration is '.. c:var:: int data'.
/.../sphinx/doc/usage/domains/c.rst:232: WARNING: Duplicate C declaration, also defined at usage/domains/c:232.
Declaration is '.. c:function:: int f(double k)'.

sorry for mentioning it here)