Temporarily revert path compression

For reasons I don't understand yet, this causes an issue when trying to
boot yjit-bench. Temporarily revert it.

Author: tekknolagi

zjit/src/hir.rs

@@ -752,7 +752,9 @@ impl Function {
         macro_rules! find {
             ( $x:expr ) => {
                 {
-                    self.union_find.borrow_mut().find($x)
+                    // TODO(max): Figure out why borrow_mut().find() causes `already borrowed:
+                    // BorrowMutError`
+                    self.union_find.borrow().find_const($x)
                 }
             };
         }