Modify OSV parsing to collect PyPa data correctly

[michaelehab]

Currently, the OSV logic for parsing advisories does not work with all PyPa file structures.
For example, it handles https://github.com/pypa/advisory-database/blob/main/vulns/jinja2/PYSEC-2014-82.yaml correctly but fails to handle https://github.com/pypa/advisory-database/blob/main/vulns/aamiles/PYSEC-2022-43066.yaml
This is mainly because of the different file structures for the affected packages, the OSV parsing logic should handle the case of the other file structure as well.