Replace unpinned actions with pinned action

.github/workflows/main.yml

@@ -1,30 +1,22 @@
 name: Rust Build
-
 on:
   push:
-    branches: [ main ]
+    branches: [main]
   pull_request:
-    branches: [ main ]
-
+    branches: [main]
 env:
   CARGO_TERM_COLOR: always
-
 jobs:
   build:
-
     runs-on: ubuntu-latest
-
     steps:
-    - name: Checkout code
-      uses: actions/checkout@v2
-
-    - name: Install Rust
-      run: |
-        curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
-        source $HOME/.cargo/env
-
-    - name: Build
-      run: cargo build --verbose
-
-    - name: Run tests
-      run: cargo test --verbose
+      - name: Checkout code
+        uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2
+      - name: Install Rust
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+          source $HOME/.cargo/env
+      - name: Build
+        run: cargo build --verbose
+      - name: Run tests
+        run: cargo test --verbose