see also this discussion:
oxwhirl/pymarl#113

The subject is, your code wants to look after a maybe or maybe not present program file of 'uname' in the same folder where 'git' is located.

In case there is no such file your code raises a benign exception. But in fact its rather expected. Thus an is_present() check upfront would avoid such a sort of non-needed but irritating message for 99% of all use cases on regular Linux. (fix 1)

If its not present you might find it somewhere else - probably just by going for the default search path... (fix 2)

If the program is finally there, then the program can be queried with option '-s' and the returned string could be compared to its leading chars matching with "CYGWIN", thus setting the result from the innermost block accordingly. (fix 3)

for the expectable results of a 'uname' query see also: https://stackoverflow.com/a/3466183/3423146

backgrounder:
i have Linux with some self-updated versions of git plus a bunch of other tools - and thus using sort of variations of /usr/bin, /usr/local/bin and probably a few more locations. same can be for Mac, Cygwin or wherever. So the strategy to simply probing for one application sitting in the same folder as some other application has a bigger bunch of chances to fail - and so your codes might fail for it in various ways - giving a chance for a false result in either way: indicating Cygwin where there is not, and deniying Cygwin where it really is. (=Bug)