run-tests: catch a Windows specific error when testing for a free socket I'm not sure why this only happens with py3, but this error code doesn't map to any of the 3 currently being handled, and kills `run-tests.py` before it can run any tests when it happens: OSError: [WinError 10013] An attempt was made to access a socket in a way forbidden by its access permissions The documentation[1] says this can happen if another process is bound to the address with exclusive access. This seems to keep it happy. [1] https://docs.microsoft.com/en-us/windows/win32/winsock/windows-sockets-error-codes-2 Differential Revision: https://phab.mercurial-scm.org/D9816