variant rendering is missing the "dialect-specific variant first" use case

[zzzeek]

Discussed in #1584

    def test_render_reverse_variant(self):
        self.autogen_context.opts["user_module_prefix"] = None

        type_ = (
            LONGTEXT().with_variant(String(10), "oracle")
        )

        eq_ignore_whitespace(
            autogenerate.render._repr_type(type_, self.autogen_context),
            "mysql.LONGTEXT()."
            "with_variant(sa.String(length=10), 'oracle')",
        )

skips the variants due to dialect check first

[sqla-tester]

Mike Bayer has proposed a fix for this issue in the main branch:

check for variants (recursion branch) first in all cases https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/5639