Consider changing sy-sysid from ABC to something else

[fabianlupa]

abapGit/abapGit#6653 (comment)

The API to check if the runtime is open-abap or something else seems to be checking for sy-sysid = 'ABC'. ABC is a valid system id as far as I know. If I were SAP I would name my glossary / SAPterm production system ABC :P

To me it would make sense to use an ID that is not useable in a normal system. Either by using a reserved name or by using special characters or a number at the first position. I don't think either is allowed normally.