Update to Rust 1.76 (#4411)

Motivation: I want to replace `cargo-cranky` with workspace lints, first
available in Rust 1.74.
However, `cargo doc` would hange on `wgpu` and `wgpu-core` on 1.74 and
1.75… so now we're on 1.76.
I think this is fine - when 1.78 is released next week we're still two
versions behind the bleeding edge.

…and the branch name is just wrong 🤦

crates/eframe/src/native/run.rs

@@ -391,6 +391,8 @@ pub fn run_glow(
     mut native_options: epi::NativeOptions,
     app_creator: epi::AppCreator,
 ) -> Result<()> {
+    #![allow(clippy::needless_return_with_question_mark)] // False positive
+
     use super::glow_integration::GlowWinitApp;
 
     #[cfg(not(target_os = "ios"))]
@@ -414,6 +416,8 @@ pub fn run_wgpu(
     mut native_options: epi::NativeOptions,
     app_creator: epi::AppCreator,
 ) -> Result<()> {
+    #![allow(clippy::needless_return_with_question_mark)] // False positive
+
     use super::wgpu_integration::WgpuWinitApp;
 
     #[cfg(not(target_os = "ios"))]