Bump indexmap

`swap` has been deprecated in favour of `swap_remove` - the behaviour
is the same though.

compiler/rustc_borrowck/src/used_muts.rs

@@ -58,7 +58,8 @@ impl GatherUsedMutsVisitor<'_, '_, '_> {
         // be those that were never initialized - we will consider those as being used as
         // they will either have been removed by unreachable code optimizations; or linted
         // as unused variables.
-        self.never_initialized_mut_locals.remove(&into.local);
+        // FIXME(#120456) - is `swap_remove` correct?
+        self.never_initialized_mut_locals.swap_remove(&into.local);
     }
 }