Fix [needless_return] false negative when returned expression borrows a value

Fixes #12907

changelog: Fix [`needless_return`] false negative when returned expression borrows a value

tests/ui/needless_return.fixed

@@ -355,4 +355,8 @@ fn conjunctive_blocks() -> String {
     ({ "a".to_string() } + "b" + { "c" })
 }
 
+fn issue12907() -> String {
+    "".split("").next().unwrap().to_string()
+}
+
 fn main() {}

tests/ui/needless_return.rs

@@ -365,4 +365,8 @@ fn conjunctive_blocks() -> String {
     return { "a".to_string() } + "b" + { "c" };
 }
 
+fn issue12907() -> String {
+    return "".split("").next().unwrap().to_string();
+}
+
 fn main() {}

tests/ui/needless_return.stderr

@@ -665,5 +665,17 @@ LL -     return { "a".to_string() } + "b" + { "c" };
 LL +     ({ "a".to_string() } + "b" + { "c" })
    |
 
-error: aborting due to 53 previous errors
+error: unneeded `return` statement
+  --> tests/ui/needless_return.rs:369:5
+   |
+LL |     return "".split("").next().unwrap().to_string();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove `return`
+   |
+LL -     return "".split("").next().unwrap().to_string();
+LL +     "".split("").next().unwrap().to_string()
+   |
+
+error: aborting due to 54 previous errors