fix: incorrect 'find -type' argument used on MacOS

[acordiner]

Within write_source_file(), an incorrect find argument is being used on MacOS to iterate over the copied files. Instead of find -type f, it is using find -type file, which produces an error:

find: Must separate multiple arguments to -type using: ','

[CLAassistant]

All committers have signed the CLA.

[gregmagolan]

Hmm. Something is fishy here. I'm able to run

$ find . -type file | wc -l
    2642

on my macbook without any issues.

[gregmagolan]

Oh I see. Some implementations of file are tolerant of the additional chars in -type but your change is correct.

[acordiner]

Thanks @gregmagolan! Any chance to get this released?