abstractJob stdin, stdout, stderr in the wf schema should be updated s.t.
$ref: "rc-5.0.yml#/$defs/file" is replaced with "type: string". Only lfn is considered in the file object, therefore unnecessary nesting can be avoided.

57 stdin:
58 $ref: "rc-5.0.yml#/$defs/file"
59 stdout:
60 $ref: "rc-5.0.yml#/$defs/file"
61 stderr:
62 $ref: "rc-5.0.yml#/$defs/file"