Disable tests involving ZLIB on Windows for pg_receivewal

Disable tests involving ZLIB on Windows for pg_receivewal

As reported by buildfarm member bowerbird, those tests are unstable on
Windows.  The failure produced there points to a problem with gzflush(),
that fails to sync a file freshly-opened, with a gzFile properly
opened.  While testing this myself with MSVC, I bumped into a different
error where a file could simply not be opened, so this makes me rather
doubtful that testing this area on Windows is a good idea if this
finishes with random concurrency failures.  This requires more
investigation, and keeping this buildfarm member red is not a good thing
in the long-term, so for now this just disables this set of tests on
Windows.

Discussion: https://postgr.es/m/YPDLz2x3o1aX2wRh@paquier.xyz