fix: executor arg of RawSql methods can have looser bound

[tisonkun]

The original code has an unnecessary lifetime bound 'q: 'e.

We have a code snippet like:

    let res = sqlx::raw_sql(&insert_sql)
        .execute(&mut **txn)
        .await
        .change_context_lazy(make_error)?;

failed with: implementation of `std::marker::Send` is not general enough in several caller layers outside.

while change to:

    let res = txn
        .execute(&insert_sql)
        .await
        .change_context_lazy(make_error)?;

works.

A brief is that the txn's lifetime bound to the outer struct, so as long as the returned future is bound to that lifetime, rustc knows it's send for all outer struct's lifetime.

However, with .execute(&mut **txn), the new lifetime c is resolved to e where 'q: 'e and then the return future lifetime is 'e. Now rustc doesn't know the relation of the lifetimes, and failed to compile.

[tisonkun]

I just find that the implementation of sqlx::query(...).execute(&mut **txn) is correct and we can simply align the code as in the second commit.

[joeydewaal]

Looks like there is already a fix for this (#3613)

[tisonkun]

@joeydewaal Looks correct. I'd leave to @abonander to manage both PRs. Closing this is fine.

[abonander]

I believe I tried this approach and it didn't fix the minimal reproduction I came up with. Since this doesn't have a reproduction to show that it fixes the problem, and my PR makes the API match the Query{As, Scalar} types, I'm going to close in favor of #3613.