Investigate error handling in copy_directory.py

[berland]

There seems to be an error in the exception handling of copy_directory.py, at least this output was retrieved in an everest test case in the file copy_directory.stderr.0 where the original error (EGG_FLOW.DATA not being present) is correct.

Traceback (most recent call last):
  File "/private/havb/projects/ert/src/ert/resources/shell_scripts/copy_directory.py", line 33, in <module>
    copy_directory(src_path, target_path)
  File "/private/havb/projects/ert/src/ert/resources/shell_scripts/copy_directory.py", line 21, in copy_directory
    shutil.copytree(src_path, target_path, dirs_exist_ok=True)
  File "/usr/lib64/python3.11/shutil.py", line 561, in copytree
    return _copytree(entries=entries, src=src, dst=dst, symlinks=symlinks,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.11/shutil.py", line 515, in _copytree
    raise Error(errors)
shutil.Error: [('/private/havb/projects/ert/test-data/everest/egg/everest/model/../../eclipse/include/realizations/realization-0/eclipse/model/EGG_FLOW.DATA', 'eclipse/model/EGG_FLOW.DATA', "[Errno 2] No such file or directory: '/private/havb/projects/ert/test-data/everest/egg/everest/model/../../eclipse/include/realizations/realization-0/eclipse/model/EGG_FLOW.DATA'")]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/private/havb/projects/ert/src/ert/resources/shell_scripts/copy_directory.py", line 36, in <module>
    f"COPY_DIRECTORY failed with the following error: {''.join(e.args[0])}"
                                                       ^^^^^^^^^^^^^^^^^^
TypeError: sequence item 0: expected str instance, tuple found
copy_directory.stderr.0 (END)