tests don't compile on stable Rust: std::hash::RandomState only present on nightly

[decathorpe]

It looks like there might be a problem in nightly Rust, where RandomState is available under a different module / import path than on stable Rust.

On Rust stable, RandomState is only available at std::collections::hash_map::RandomState, but on Rust nightly, it's also available at std::hash::RandomState (which is what is now used by serde_json's tests), but this looks like a mistake.

Not sure why your CI didn't catch that serde_json tests currently don't compile on stable Rust (i.e. this fails: cargo +stable test):

error[E0433]: failed to resolve: could not find `RandomState` in `hash`
    --> tests/test.rs:2494:27
     |
2494 |     let rand = std::hash::RandomState::new();
     |                           ^^^^^^^^^^^ could not find `RandomState` in `hash`
     |
help: consider importing this struct
     |
23   + use std::collections::hash_map::RandomState;
     |
help: if you import `RandomState`, refer to it directly
     |
2494 -     let rand = std::hash::RandomState::new();
2494 +     let rand = RandomState::new();
     |

warning: unused import: `std::hash::BuildHasher`
  --> tests/test.rs:37:5
   |
37 | use std::hash::BuildHasher;
   |     ^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default