Don't use "set -x" for "pytest" command on Cygwin

The omission of "set -x" was intentional and is currently necessary
on Cygwin (but not on Ubuntu), per aafb92a.

Author: EliahKagan

.github/workflows/cygwin-test.yml

@@ -68,5 +68,4 @@ jobs:
 
     - name: Test with pytest
       run: |
-        set -x
         /usr/bin/python -m pytest