fix-ci: move from unmaintained actions-rs to a maintained alternative

Summary:
Unfortunately `actions-rs` is [unmaintained](actions-rs/toolchain#216) and I am trying to advocate a move from actions-rs to its maintained alternative such as https://github.com/dtolnay/rust-toolchain across the community.

X-link: facebook/hhvm#9369

Reviewed By: dtolnay

Differential Revision: D46326694

Pulled By: dtolnay

fbshipit-source-id: 2f08553539fba083e5ec90662328d69b78e19b44

build/fbcode_builder/getdeps.py

@@ -1043,11 +1043,7 @@ def write_job_for_platform(self, platform, args):  # noqa: C901
                 if m != manifest:
                     if m.name == "rust":
                         out.write("    - name: Install Rust Stable\n")
-                        out.write("      uses: actions-rs/toolchain@v1\n")
-                        out.write("      with:\n")
-                        out.write("        toolchain: stable\n")
-                        out.write("        default: true\n")
-                        out.write("        profile: minimal\n")
+                        out.write("      uses: dtolnay/rust-toolchain@stable\n")
                     else:
                         ctx = loader.ctx_gen.get_context(m.name)
                         if m.get_repo_url(ctx) != main_repo_url: