build: Set the crate MSRV to silence Clippy warnings

Adopt the same MSRV policy as PyO3.

Author: ravenexp

Cargo.toml

@@ -2,6 +2,7 @@
 name = "python3-dll-a"
 version = "0.2.14"
 edition = "2021"
+rust-version = "1.63"
 description = "Standalone python3(y)(t).dll import library generator"
 repository = "https://github.com/PyO3/python3-dll-a"
 authors = ["Sergey Kvachonok <[email protected]>", "messense <[email protected]>", "Adam Reichold <[email protected]>"]