Turn off two tests broken due to #4108

tests/ui/crashes/used_underscore_binding_macro.rs

@@ -1,5 +1,7 @@
 // run-pass
 
+// FIXME(#4108)
+/*
 #![allow(clippy::useless_attribute)] //issue #2910
 
 #[macro_use]
@@ -17,5 +19,6 @@ struct MacroAttributesTest {
 fn macro_attributes_test() {
     let _ = MacroAttributesTest { _foo: 0 };
 }
+*/
 
 fn main() {}

tests/ui/serde.rs

@@ -1,3 +1,6 @@
+// FIXME(#4108)
+
+/*
 #![warn(clippy::serde_api_misuse)]
 #![allow(dead_code)]
 
@@ -43,5 +46,5 @@ impl<'de> serde::de::Visitor<'de> for B {
         unimplemented!()
     }
 }
-
+*/
 fn main() {}

tests/ui/serde.stderr

@@ -1,15 +0,0 @@
-error: you should not implement `visit_string` without also implementing `visit_str`
-  --> $DIR/serde.rs:39:5
-   |
-LL | /     fn visit_string<E>(self, _v: String) -> Result<Self::Value, E>
-LL | |     where
-LL | |         E: serde::de::Error,
-LL | |     {
-LL | |         unimplemented!()
-LL | |     }
-   | |_____^
-   |
-   = note: `-D clippy::serde-api-misuse` implied by `-D warnings`
-
-error: aborting due to previous error
-