validation of enumerated values does not support multiple values

[dwikler]

I noticed that when multiple values are encoded for the MR Image Scanning Sequence attribute, an error is reported even if both values match the enumerated values.
Here is the output:

Module "MR Image":
Tag (0018,0020) (Scanning Sequence) value is not allowed (value: ['SE', 'EP'], allowed: SE, IR, GR, EP, RM)

The current implementation of enumerated values may be limited to single value only.

[mrbean-bremen]

I made a new patch release with the fix, please check!