Raise minimum version for preserve_order feature to Rust 1.65

Required by hashbrown 0.15.1.

    error: package `hashbrown v0.15.1` cannot be built because it requires rustc 1.65.0 or newer, while the currently active rustc version is 1.64.0

Author: dtolnay

.github/workflows/ci.yml

@@ -43,7 +43,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [beta, 1.64.0, 1.56.1]
+        rust: [beta, 1.65.0, 1.56.1]
         os: [ubuntu]
         include:
           - rust: stable