Add pypy3.7 7.3.5 to s390x

[messense]

Not sure why #1103 omits s390x, https://downloads.python.org/pypy/ has PyPy3 s390x release.

[henryiii]

@mayeut is out for a couple of weeks, I think he's back next week. Looks like from the Travis run that libncursesw.so is missing for s390x.

[mayeut]

@messense, the relevant discussion for #1103 not including s390x is there: #1099 (comment)

In short, the s390x binaries of PyPy are not portable across distros.

I honestly thought it would work on manylinux2014 but the failure in CI tends to prove otherwise.