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/egui_extras/src/table.rs

@@ -131,7 +131,7 @@ impl Column {
         self
     }
 
-    /// Allowed range of movement (in points), if in a resizable [`Table`](crate::table::Table).
+    /// Allowed range of movement (in points), if in a resizable [`Table`].
     #[inline]
     pub fn range(mut self, range: impl Into<Rangef>) -> Self {
         self.width_range = range.into();