Disable opt in incremental test.

Author: cjgillot

tests/incremental/string_constant.rs

@@ -1,5 +1,5 @@
 // revisions: cfail1 cfail2
-// compile-flags: -Z query-dep-graph
+// compile-flags: -Z query-dep-graph -Copt-level=0
 // build-pass (FIXME(62277): could be check-pass?)
 
 #![allow(warnings)]
@@ -17,7 +17,7 @@ pub mod x {
     }
 
     #[cfg(cfail2)]
-    #[rustc_clean(except = "hir_owner_nodes,promoted_mir,optimized_mir", cfg = "cfail2")]
+    #[rustc_clean(except = "hir_owner_nodes,promoted_mir", cfg = "cfail2")]
     pub fn x() {
         println!("{}", "2");
     }