Rename test

tests/ui/lint/unused/issue-119383-if-let-guard.stderr

@@ -1,11 +1,11 @@
 error: unused variable: `b`
-  --> $DIR/issue-119383.rs:6:24
+  --> $DIR/issue-119383-if-let-guard.rs:6:24
    |
 LL |         () if let Some(b) = Some(()) => {}
    |                        ^ help: if this is intentional, prefix it with an underscore: `_b`
    |
 note: the lint level is defined here
-  --> $DIR/issue-119383.rs:2:9
+  --> $DIR/issue-119383-if-let-guard.rs:2:9
    |
 LL | #![deny(unused_variables)]
    |         ^^^^^^^^^^^^^^^^