Log Message:
libxml2 & py-libxml2: update to 2.10.4

v2.10.4: Apr 11 2023

### Security

- [CVE-2023-29469] Hashing of empty dict strings isn't deterministic
- [CVE-2023-28484] Fix null deref in xmlSchemaFixupComplexType
- schemas: Fix null-pointer-deref in xmlSchemaCheckCOSSTDerivedOK

### Regressions

- SAX2: Ignore namespaces in HTML documents
- io: Fix "buffer full" error with certain buffer sizes