Refactor if-else binding scope management

The explicit scope management within the `if`/`else` binding logic was
redundant.
The `bind` function recursively handles scope creation and destruction
for
expressions, making manual scope manipulation here unnecessary and
error-prone.

src/ast/compiler/binder.rs

@@ -243,16 +243,11 @@ impl Binder {
                 else_br,
             } => {
                 let cond = self.bind(cond.as_ref(), ExprContext::Expression, diag);
-
-                self.functions.last_mut().unwrap().push_scope();
                 let then_br = self.bind(then_br.as_ref(), ctx, diag);
-                self.functions.last_mut().unwrap().pop_scope();
 
                 let mut else_br_bound = None;
                 if let Some(e) = else_br {
-                    self.functions.last_mut().unwrap().push_scope();
                     else_br_bound = Some(Rc::new(self.bind(e, ctx, diag)));
-                    self.functions.last_mut().unwrap().pop_scope();
                 }
 
                 self.make_node(