fix(tvix/eval): don't increase with_stack_size in scope inherits

There was probably a misunderstanding somewhere about the
with_stack_size being related to how far away it is from the with, but
it is about whether there is a with at all.

This broke a warning (`UselessInherit`), and may actually have let to
more inefficient codegen in some cases.

Change-Id: I08338ea59ae39dad01ca8a4e09d934a936cdea2f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7762
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/eval/src/compiler/scope.rs

@@ -210,7 +210,7 @@ impl Scope {
         Self {
             poisoned_tokens: self.poisoned_tokens.clone(),
             scope_depth: self.scope_depth + 1,
-            with_stack_size: self.with_stack_size + 1,
+            with_stack_size: self.with_stack_size,
             ..Default::default()
         }
     }