Bump MSRV to 1.63

Author: djc

.github/workflows/rust.yml

@@ -90,7 +90,7 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: 1.54.0
+          toolchain: 1.63.0
           override: true
       - run: rustup component add clippy
       - uses: actions-rs/cargo@v1