Update Rust toolchain installation method (#716)

* Update Rust toolchain installation method

Replaced actions-rs/toolchain with rustup for toolchain installation.

* Update builds.yml

* Add workflow_dispatch trigger to builds.yml

Author: cloudwebrtc

.github/workflows/builds.yml

@@ -25,6 +25,7 @@ on:
     paths:
       - livekit/**
       - libwebrtc/**
+  workflow_dispatch:
 
 env:
   CARGO_TERM_COLOR: always
@@ -80,10 +81,9 @@ jobs:
         run:  |
           sudo apt install -y libva-dev libdrm-dev libnvidia-compute-570 libnvidia-decode-570 nvidia-cuda-dev -y
 
-      - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: stable
-          target: ${{ matrix.target }}
+      - name: Install Rust toolchain.
+        run: |
+          rustup target add ${{ matrix.target }}
 
       - name: Build (Cargo)
         if: ${{ !contains(matrix.target, 'android') }}