There are currently issues where the non-.exe-suffixed files can't be
copied into the `artifacts` folder; `cp` claims "File exists".
Previously this worked but the suffix was added by Cygwin so all files
in `artifacts` had a `.exe` suffix anyway.
This is evidently intended, though non-intuitive, behavior:
https://sourceware.org/legacy-ml/cygwin/2009-08/msg00293.html
> On Cygwin, you should avoid having a file "foo" and a file "foo.exe"
> in the same directory at all cost to avoid puzzeling POSIX borderline
> behaviour like this. What you do is essentially in the "not
> supported" class of problems.
> [...] Cygwin does not check for a file "foo", if the name of the file
> is explicitely given as "foo.exe".
Apparently something similar was addressed in PR #20926; the current
code installs files with both suffixes, but that fix contradicts the
info above and now has broken.
This PR changes the code to only install .exe-suffixed files, as opposed
to only non-.exe-suffixed files, which was the behavior before that PR.
