Unable to use f-string in SqlAlchemy ORM

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* **asyncpg version**: 0.23.0
* **PostgreSQL version**: 12
* **Python version**: 3.9.4
* **Platform**: OSX
* **Do you use pgbouncer?**: No
* **Did you install asyncpg with pip?**: pipenv
* **If you built asyncpg locally, which version of Cython did you use?**: N/A
* **Can the issue be reproduced under both asyncio and
[uvloop](https://github.com/magicstack/uvloop)?**: N/A

I'm trying to build a SQL statement with LIKE expression and a pattern but I'm getting an error.

Here is what I had in the code originally:
```
statement = select(Customer).options(sqlalchemy.orm.joinedload(Customer.transactions)).where(Customer.l_name.ilike(name))
```
and this worked great.

But if I want to use this statement with a % pattern like this:

```
statement = f'select(Customer).options(sqlalchemy.orm.joinedload(Customer.transactions)).where(Customer.l_name.ilike("%{name}%"))'
```

I get this error:

```
sqlalchemy.exc.ProgrammingError: (sqlalchemy.dialects.postgresql.asyncpg.ProgrammingError) : syntax error at or near "("
[SQL: select(Customer).options(sqlalchemy.orm.joinedload(Customer.transactions)).where(Customer.l_name.ilike("%%turing%%"))]
```

It does substitute the variable with a parameter but for some reason it adds an extra pair of percent signs and crashes.
How can I solve this problem?

No asyncpg file, test, or entry point is named. Start with the supplied SQLAlchemy expression and generated SQL, then verify whether the behavior reproduces in asyncpg or comes from constructing the ORM statement as a string; confirm the result against the listed PostgreSQL and asyncpg versions.

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