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/macos/mod.rs

@@ -74,7 +74,7 @@ impl Deref for Window {
     type Target = WinitWindow;
     #[inline]
     fn deref(&self) -> &Self::Target {
-        &*self.window
+        &self.window
     }
 }