HPCC-10527 Can't run the regression suite from another directory

Resove regress.json file location path from regress main script path.

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>
Merge pull request #5216 from AttilaVamos/HPCC-10527-fix

HPCC-10527 Can't run the regression suite from another directory

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>