Log Message:
py-yaml: updated to 5.3

5.3:
Use `is` instead of equality for comparing with `None`
fix typos and stylistic nit
Fix up small typo
Fix handling of __slots__
Allow calling add_multi_constructor with None
Add use of safe_load() function in README
Fix reader for Unicode code points over 0xFFFF
Enable certain unicode tests when maxunicode not > 0xffff
Use full_load in yaml-highlight example
Document that PyYAML is implemented with Cython
Fix for Python 3.10
increase size of index, line, and column fields
remove some unused imports
Create timezone-aware datetimes when parsed as such
Add tests for timezone