Use cargo generate-lockfile to update JikesRVM's Cargo.lock (#996)

`auto-merge.yml` uses `cargo build` to generate lockfile for most
bindings. But this does not work for JikesRVM:
1. JikesRVM uses `--target i686-unknown-linux-gnu` which is not
installed automatically when running `cargo build`.
2. JikesRVM's cargo project uses some Rust source files that are
generated during building JikesRVM. So we cannot build the cargo project
alone from a fresh repo clone. We have to do a full build.

As a workaround, we use `cargo generate-lockfile` for JikesRVM. `cargo
generate-lockfile` will update the version of dependencies. But we do
not have a better option for JikesRVM

.github/workflows/auto-merge.yml

@@ -50,7 +50,11 @@ jobs:
       base_repo: mmtk/mmtk-jikesrvm
       ref: ${{ needs.binding-refs.outputs.jikesrvm_binding_ref }}
       core_commit: ${{ needs.get-merged-pr.outputs.commit }}
-      update_lockfile: cargo build --features nogc --target i686-unknown-linux-gnu
+      # `cargo generate-lockfile` will update other dependencies. We avoid using it for the bindings.
+      # But we do not have a good option for JikesRVM. The Rust project in JikesRVM needs some source files
+      # that are generated during its build process. Unless we want to do a full build for JikesRVM, we cannot
+      # use `cargo build`. So use `cargo generate-lockfile` instead.
+      update_lockfile: cargo generate-lockfile
     secrets: inherit
 
   check-merge-v8-pr: