upb vulnerabilities (OSS-Fuzz)

2 vulnerabilities.

• upb OSS-Fuzz Segv on unknown address in upb_MiniTable_SetSubEnum OSV-2022-1002 Fix available No scoreSeptember 30, 2022
• upb OSS-Fuzz Bad-cast to const upb_tabent' (aka 'const struct _upb_tabent')insert OSV-2022-412 Fix available No scoreMay 17, 2022