Always skip recovery SysV shared memory tests on Windows

The test for SysV support currently involves looking for the perl
modules IPC::SharedMem and IPC::SysV. However, the perl on msys2 has
these modules but the tests fail. Therefore, force skipping the tests on
Windows platforms unconditionally.

Discussion: https://postgr.es/m/176e86ba-1a46-9d8c-5ae4-9865a463b411@2ndQuadrant.com