test: update tests for manual_instant_elapsed lint

Author: nfejzic

tests/ui/manual_instant_elapsed.fixed

@@ -1,6 +1,7 @@
 // run-rustfix
 #![warn(clippy::manual_instant_elapsed)]
 #![allow(clippy::unnecessary_operation)]
+#![allow(clippy::unchecked_duration_subtraction)]
 #![allow(unused_variables)]
 #![allow(unused_must_use)]
 

tests/ui/manual_instant_elapsed.rs

@@ -1,6 +1,7 @@
 // run-rustfix
 #![warn(clippy::manual_instant_elapsed)]
 #![allow(clippy::unnecessary_operation)]
+#![allow(clippy::unchecked_duration_subtraction)]
 #![allow(unused_variables)]
 #![allow(unused_must_use)]
 

tests/ui/manual_instant_elapsed.stderr

@@ -1,13 +1,13 @@
 error: manual implementation of `Instant::elapsed`
-  --> $DIR/manual_instant_elapsed.rs:17:20
+  --> $DIR/manual_instant_elapsed.rs:18:20
    |
 LL |     let duration = Instant::now() - prev_instant;
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `prev_instant.elapsed()`
    |
    = note: `-D clippy::manual-instant-elapsed` implied by `-D warnings`
 
 error: manual implementation of `Instant::elapsed`
-  --> $DIR/manual_instant_elapsed.rs:26:5
+  --> $DIR/manual_instant_elapsed.rs:27:5
    |
 LL |     Instant::now() - *ref_to_instant; // to ensure parens are added correctly
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(*ref_to_instant).elapsed()`