Auto merge of #50546 - kennytm:rollup, r=kennytm

Rollup of 11 pull requests

Successful merges:

 - #49988 (Mention Result<!, E> in never docs.)
 - #50148 (turn `ManuallyDrop::new` into a constant function)
 - #50456 (Update the Cargo submodule)
 - #50460 (Make `String::new()` const)
 - #50464 (Remove some transmutes)
 - #50505 (Added regression function match value test)
 - #50511 (Add some explanations for #[must_use])
 - #50525 (Optimize string handling in lit_token().)
 - #50527 (Cleanup a `use` in a raw_vec test)
 - #50539 (Add more logarithm constants)
 - #49523 (Update RELEASES.md for 1.26.0)

Failed merges:

1 files changed, 2 insertions, 1 deletions

diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index 2f84d5f7f86..da9afdd2ca3 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -380,7 +380,8 @@ impl String {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn new() -> String {
+    #[rustc_const_unstable(feature = "const_string_new")]
+    pub const fn new() -> String {
         String { vec: Vec::new() }
     }