Only build, but don't run tests in MSRV CI (#2558)

* Only build, but don't run tests in MSRV CI

Since the MSRV of development dependencies can easily be bumped without it affecting the MSRV of the published version of `winit`

* Run clippy on stable Rust instead of MSRV Rust

clippy inspects the `rust-version` field, and only suggests changes that conform to that.

src/platform_impl/linux/x11/event_processor.rs

@@ -1228,7 +1228,7 @@ impl<T: 'static> EventProcessor<T> {
                                                 new_monitor.scale_factor,
                                                 width,
                                                 height,
-                                                &*window.shared_state_lock(),
+                                                &window.shared_state_lock(),
                                             );
 
                                             let window_id = crate::window::WindowId(*window_id);