fix: implement AnyConnectionBackend::as_migrate for databases

sqlx-mysql/src/any.rs

@@ -62,6 +62,13 @@ impl AnyConnectionBackend for MySqlConnection {
         Connection::should_flush(self)
     }
 
+    #[cfg(feature = "migrate")]
+    fn as_migrate(
+        &mut self,
+    ) -> sqlx_core::Result<&mut (dyn sqlx_core::migrate::Migrate + Send + 'static)> {
+        Ok(self)
+    }
+
     fn fetch_many<'q>(
         &'q mut self,
         query: &'q str,