Auto merge of #70371 - Centril:rollup-ywi1vo3, r=Centril

Rollup of 8 pull requests

Successful merges:

 - #70023 (clean up E0436 explanation)
 - #70234 (#[track_caller] on core::ops::{Index, IndexMut}.)
 - #70241 (Miri: move ModifiedStatic to ConstEval errors)
 - #70342 (IoSlice/IoSliceMut should be Send and Sync)
 - #70350 (Request "-Z unstable-options" for unstable options)
 - #70355 (Clean up E0454)
 - #70359 (must_use on split_off)
 - #70368 (Mark hotplug_codegen_backend as ignore-stage1)

Failed merges:

r? @ghost

1 files changed, 2 insertions, 2 deletions

diff --git a/src/liballoc/tests/string.rs b/src/liballoc/tests/string.rs
index 08859b2b24b..d2f09eb4a75 100644
--- a/src/liballoc/tests/string.rs
+++ b/src/liballoc/tests/string.rs
@@ -266,14 +266,14 @@ fn test_split_off_empty() {
 fn test_split_off_past_end() {
     let orig = "Hello, world!";
     let mut split = String::from(orig);
-    split.split_off(orig.len() + 1);
+    let _ = split.split_off(orig.len() + 1);
 }
 
 #[test]
 #[should_panic]
 fn test_split_off_mid_char() {
     let mut orig = String::from("山");
-    orig.split_off(1);
+    let _ = orig.split_off(1);
 }
 
 #[test]