[FIX] website, test_website: prevent fuzzy search to crash with inherits

This commit ensures that when searching on a `inherits` field of
a model (like `name` of `website.page`), it works properly when
`pg_trgm` is activated.
Indeed, `name` is a field of `website.page` record but only at the ORM
level, not in SQL, due to how `inherits` works.

So, when the `pg_trgm` extension is enabled, it will switch from ORM
queries to raw SQL query (to use the native SQL similarity feature and
not our custom python/orm one, as obviously the SQL one is better, more
powerfull/accurate and faster).
But this will actually make the code fail when searching on fields from
a model which has `inherits` and that you search on that `inherits`
model fields.

Note that in 15.2, the `pg_trgm` extension is auto installed when
possible thanks to [1] and [2].

[1]: https://github.com/odoo/odoo/commit/eedf37d6e286b995c47b946be1a6b66817094eff
[2]: https://github.com/odoo/odoo/commit/75e6b645acdc95aece506ce0249fd0760838281c



opw-3063592

closes odoo/odoo#106879

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>