Add lockfile

These are not used by CI but are hopefully useful for testing with
Nix.

The CI here is old as hell. Just to get things working create a lock
file, copy it into place, and the use `cargo --locked` anyplace that
will be run by the MSRV job so it doesn't get updated.

Author: tcharding

.github/workflows/rust.yml

@@ -159,7 +159,7 @@ jobs:
       - name: Running address sanitizer
         env:
           DO_ASAN: true
-        run: cd hashes && ./contrib/test.sh
+        run: cp Cargo-recent.lock Cargo.lock && cd hashes && ./contrib/test.sh
 
   WASM:
     name: WebAssembly Build # hashes crate only.
@@ -172,4 +172,4 @@ jobs:
       - name: Running WASM build
         env:
           DO_WASM: true
-        run: cd hashes && ./contrib/test.sh
+        run: cp Cargo-recent.lock Cargo.lock && cd hashes && ./contrib/test.sh