tests: add data validation for YAML files

[stefanomunarini]

Related comment: https://github.com/ietf-ribose/bibxml-service/issues/228#issuecomment-1175688407

[codecov]

Codecov Report

Merging #25 (5e71839) into main (ad857f3) will increase coverage by 3.31%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   92.95%   96.27%   +3.31%     
==========================================
  Files          22       22              
  Lines         767      805      +38     
==========================================
+ Hits          713      775      +62     
+ Misses         54       30      -24     

Impacted Files	Coverage Δ
relaton/tests/test_serializers.py	100.00% <100.00%> (ø)
relaton/models/bibdata.py	98.79% <0.00%> (+2.40%)	⬆️
relaton/serializers/bibxml/__init__.py	93.54% <0.00%> (+3.22%)	⬆️
relaton/serializers/bibxml/reference.py	80.61% <0.00%> (+4.08%)	⬆️
relaton/models/dates.py	92.10% <0.00%> (+5.26%)	⬆️
relaton/serializers/bibxml/anchor.py	100.00% <0.00%> (+10.00%)	⬆️
relaton/serializers/bibxml/authors.py	98.30% <0.00%> (+22.03%)	⬆️

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[ronaldtse]

Tests passing and merging.