Update compiler version expected that seems to be embedded in CHECK line of...

Update compiler version expected that seems to be embedded in CHECK line of test at llvm/test/CodeGen/SystemZ/zos-ppa2.ll.

The test contains a CHECK line which verifies an .ascii line which originally checks
for 18001970010100000000. After the bump of the compiler version to 19, the test
started to fail with the string now being 19001970010100000000.

This should fix this failing test on bots.