V6.3-012 GTM-9182 test case - Appropriate edit checking on path/file length for MUPIP BACKUP

Release note says:

MUPIP BACKUP issues FILENAMETOOLONG when the backup file path size exceeds the maximum allowed by GTM, 255 bytes. Previously, MUPIP BACKUP could at least partially execute in spite of file paths that exceeded the maximum length allowed by GTM. (GTM-9182)