Auto merge of #7738 - JohnTitor:issue-none, r=ehuss

Use issue = "none" instead of "0"

Replace `issue = "0"` with `"none"`

CC: rust-lang/rust#67496

Author: bors

tests/testsuite/mock-std/src/libtest/lib.rs

@@ -1,6 +1,6 @@
 #![feature(staged_api)]
 #![feature(test)]
-#![unstable(feature = "test", issue = "0")]
+#![unstable(feature = "test", issue = "none")]
 
 extern crate test;