packer - Switch to dtolnay/rust-toolchain@stable & bump `actions/…

…[email protected]` (#4878)

Summary:
This diff switches to `dtolnay/rust-toolchain@stable` since `actions-rs/toolchain` is **NOT maintained** and bumps `actions/[email protected]`

> **Note**:
> `uses: dtolnay/rust-toolchain@stable`
> The selection of Rust toolchain is made based on the particular `rev` of this Action being requested. For example `dtolnay/rust-toolchain@nightly` pulls in the `nightly` Rust toolchain, while `dtolnay/[email protected]` pulls in `1.42.0`.

### Ref.:
- `actions-rs/toolchain` is **NOT Maintained**, issue:
actions-rs/toolchain#216
- `dtolnay/rust-toolchain@stable` usage note: https://github.com/dtolnay/rust-toolchain#example-workflow
- `actions/[email protected]` changelog: https://github.com/actions/checkout/releases/tag/v3.5.3

## Changelog:

[GENERAL] [SECURITY] - [Actions] `packer` - Switch to `dtolnay/rust-toolchain@stable` & bump `actions/[email protected]`

Pull Request resolved: #4878

Test Plan: - Workflow should run and work as usual.

Reviewed By: lblasa

Differential Revision: D47056977

Pulled By: passy

fbshipit-source-id: 68023fcce355831314af2f31d514ed95efb7788c

.github/workflows/packer.yml

@@ -1,17 +1,19 @@
 name: Packer
-
+# This action runs on 'git push' and PRs
 on: [push, pull_request]
 
 jobs:
   build:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3.5.3
       - name: Setup toolchain
-        uses: actions-rs/toolchain@v1
-        with:
-          toolchain: 1.48.0
+        uses: dtolnay/rust-toolchain@stable
+        # The selection of Rust toolchain is made based on the particular '@rev'
+        # of this Action being requested. For example "dtolnay/rust-toolchain@nightly"
+        # pulls in the nightly Rust toolchain, while "dtolnay/[email protected]"
+        # pulls in '1.42.0'.
       - name: Test
         run: cd packer && cargo test
       - name: Format