gemini: Fix issue with builtin tool schemas (#33917)
Bennet Bo Fenner
created
Closes #33894
After #33635 Gemini Integration was broken because we now produce
`const` fields for enums, which are not supported.
Changing this to `openapi3` fixes the issue.
Release Notes:
- Fixed an issue where Gemini Models would not work because of
incompatible tool schemas