UomSymbol regex pattern rejects good values

[Here](https://github.com/ckan/ckanext-spatial/blob/9488ecd5a909026355af4f183d1cbfb3b53ab587/ckanext/spatial/validation/xml/iso19139ngdc/schema/gml/basicTypes.xsd#L134), the UomSymbol validation regex pattern `[^: \n\r\t]+` in theory is supposed to reject all chars of colon, space, newline, carriage return, and tab. But we found out it actually rejects all n, r, t chars. Values such as `decimalDegrees` and `feet` will fail the validation.

If we rewrite the pattern to an equivalent `[^:\s]+`, then all looks ok.