Malformed validation messages when they reference a nested key

[davemfish]

A validation message that references a nested key is malformed. Here a have an incorrect type for the description:

data_model:
  bands:
  - index: 1
    gdal_type: Int16
    numpy_type: int16
    nodata: -32768.0
    description: 99
    title: ''
    units: ''

Actually the problem is that the nesting here includes a list, so the message formatting raises an exception:

Traceback (most recent call last):
  File "/home/dmf/projects/geometamaker/env/bin/geometamaker", line 8, in <module>
    sys.exit(cli())
             ^^^^^
  File "/home/dmf/projects/geometamaker/env/lib/python3.12/site-packages/click/core.py", line 1161, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dmf/projects/geometamaker/env/lib/python3.12/site-packages/click/core.py", line 1082, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/home/dmf/projects/geometamaker/env/lib/python3.12/site-packages/click/core.py", line 1697, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dmf/projects/geometamaker/env/lib/python3.12/site-packages/click/core.py", line 1443, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dmf/projects/geometamaker/env/lib/python3.12/site-packages/click/core.py", line 788, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dmf/projects/geometamaker/src/geometamaker/cli.py", line 83, in validate
    echo_validation_error(error, filepath)
  File "/home/dmf/projects/geometamaker/src/geometamaker/cli.py", line 51, in echo_validation_error
    location = ', '.join(e['loc'])
               ^^^^^^^^^^^^^^^^^^^
TypeError: sequence item 2: expected str instance, int found

And naively coercing to a str leaves it looking like this,

✕ scratch/CGIAR_et0_annual_epsg_3857.tif.yml: 1 validation errors
(, ', d, a, t, a, _, m, o, d, e, l, ', ,,  , ', b, a, n, d, s, ', ,,  , 0, ,,  , ', d, e, s, c, r, i, p, t, i, o, n, ', )
    Input should be a valid string. [input_value=99, input_type=int]

Things are working okay for nested keys where all the parents are dicts, not lists. For example,

✕ scratch/CGIAR_et0_annual_epsg_3857.tif.yml: 1 validation errors
license, title
    Input should be a valid string. [input_value=0, input_type=int]