fix(tvix/eval): fix doc comment syntax where applicable

As pointed out by grfn on cl/6091

Change-Id: I28308577b7cf99dffb4a4fd3cc8783eb9ab4d0d6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6460
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/value/builtin.rs

@@ -39,7 +39,7 @@ pub struct Builtin {
     arity: usize,
     func: BuiltinFn,
 
-    // Partially applied function arguments.
+    /// Partially applied function arguments.
     partials: Vec<Value>,
 }