Rollup merge of #124978 - saethlin:ref-casting_derefs, r=Urgau,Nilstrieb

Handle Deref expressions in invalid_reference_casting

Similar to https://github.com/rust-lang/rust/pull/124908

See https://github.com/rust-lang/rust/issues/124951 for context; this PR fixes the last of the known false postiive cases with this lint that we encounter in Crater.

compiler/rustc_lint/src/reference_casting.rs

@@ -202,8 +202,10 @@ fn is_cast_to_bigger_memory_layout<'tcx>(
 
     // if the current expr looks like this `&mut expr[index]` then just looking
     // at `expr[index]` won't give us the underlying allocation, so we just skip it
-    // the same logic applies field access like `&mut expr.field`
-    if let ExprKind::Index(..) | ExprKind::Field(..) = e_alloc.kind {
+    // the same logic applies field access `&mut expr.field` and reborrows `&mut *expr`.
+    if let ExprKind::Index(..) | ExprKind::Field(..) | ExprKind::Unary(UnOp::Deref, ..) =
+        e_alloc.kind
+    {
         return None;
     }