Fix broken gitlab updates

[marcelldls]

This fixes a cryptic error that is raised when gitlab repos attempt a copier update:

[esq51579@pc0146 MY_REPO_NAME]$ copier update .
Updating to template version 4.2.0
Traceback (most recent call last):
  File "/home/esq51579/.local/bin/copier", line 8, in <module>
    sys.exit(copier_app_run())
             ^^^^^^^^^^^^^^^^
  File "/home/esq51579/.local/lib/python3.11/site-packages/plumbum/cli/application.py", line 638, in run
    inst, retcode = subapp.run(argv, exit=False)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/esq51579/.local/lib/python3.11/site-packages/plumbum/cli/application.py", line 633, in run
    retcode = inst.main(*tailargs)
              ^^^^^^^^^^^^^^^^^^^^
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/cli.py", line 425, in main
    return _handle_exceptions(inner)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/cli.py", line 70, in _handle_exceptions
    method()
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/cli.py", line 415, in inner
    with self._worker(
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 237, in __exit__
    raise value
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/cli.py", line 423, in inner
    worker.run_update()
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 914, in run_update
    self._apply_update()
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 935, in _apply_update
    with replace(
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 237, in __exit__
    raise value
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 944, in _apply_update
    old_worker.run_copy()
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 833, in run_copy
    self._ask()
  File "/home/esq51579/.local/lib/python3.11/site-packages/copier/main.py", line 497, in _ask
    raise ValueError(f"Validation error for question '{var_name}': {err_msg}")
ValueError: Validation error for question 'dls_technical_area': expected string or bytes-like object, got 'Undefined'

I test this locally with the 4.2.1b1 release using copier copy gh:epics-containers/deployment-template-argocd MY_REPO_NAME_2 -r 4.2.1b1 and then copier update . -r 4.2.1b1

Why the validator passes at copier copy time seems like a bug?

[gilesknap]

looks good. Thanks. Merging.