Bump recursion limit in diesel_tests

The attribute in `schema.rs` didn't seem to do anything. I'm not sure if
that is a regression in Rust or an oversight on our part (and the attr
wasn't necessary before).

Additionally, looking at <rust-lang/rust#41676>,
this shouldn't be necessary at all in recent nightlies (after May 7),
but without the explicit setting, it fails to compile and suggests
adding `#![recursion_limit="128"]`. If I read the code in [1] correctly,
this means it was set to 64 before.

[1]: https://github.com/rust-lang/rust/blob/5c7add7551fa093f655e76650a48564ac347c83a/src/librustc/traits/error_reporting.rs#L1150-L1156

diesel_tests/tests/lib.rs

@@ -1,3 +1,5 @@
+#![recursion_limit="1024"]
+
 extern crate quickcheck;
 #[macro_use] extern crate assert_matches;
 #[macro_use] extern crate diesel;