Add dictionary check GitHub actions

[vaitkus]

This is the standard dictionary check workflow used by all IUCr dictionary repositories. The check consists of 3 main steps:

1. Syntax check. Tests if dictionaries conform to the CIF 2.0 file syntax.
2. Semantics check. Tests if the dictionaries are valid according to the DDLm reference dictionary (formal validation) and whether they conform to a set of best practices (less formal validation).
3. Layout check. Tests if dictionaries follow the layout rules (category and data items ordering, whitespace placement, etc.) as specified in https://github.com/COMCIFS/comcifs.github.io/blob/main/accepted/ddlm_dictionary_style_guide.md.

For now, I have disabled the Layout check given that the dictionary is still early in the development.

The current version of the dictionaries fail both syntactic and semantic checks, but most issues that should be fixed were reported in the comment of PR #18. The remaining unreported issues do not prevent the dictionary from being interpreted correctly so I will report them in a separate issue.