tests `cobj-idx`, `file-lock` and `file-lock2` fail if -j option is specified

[yutaro-sakamoto]

cobj-idx, file-lock and file-lock2 in tests has option -j which implies that test suites runs concurrently.
These tests may fail if -j option is specified.

• https://github.com/opensourcecobol/opensourcecobol4j/actions/runs/24138208977/job/70432232494
• https://github.com/yutaro-sakamoto/opensourcecobol4j/actions/runs/24136243432

It seems that tests for indexed files or implementaions of them are incorrect.