Generics API Joins() fails on Oracle due to hardcoded "AS" before table alias

## GORM Playground Link

https://github.com/go-gorm/playground/pull/825

## Description

When using GORM generics Joins with a subquery and `.As("t")`, the generated SQL is:
```
LEFT JOIN (...) AS `t` ON ...
```
Oracle does not allow `AS` before table aliases. As a result, this SQL fails with a syntax error when running against Oracle DB.