Update actions/checkout action to v3

Author: renovate[bot]

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Install stable toolchain
         uses: actions-rs/toolchain@v1
@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           submodules: true