Update actions/checkout action to v3 (#104)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v2.3.4
+      - uses: actions/checkout@v3.0.2
 
       - uses: actions-rs/toolchain@v1.0.7
         with:
@@ -58,7 +58,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v2.3.4
+      - uses: actions/checkout@v3.0.2
 
       - uses: actions-rs/toolchain@v1.0.7
         with:
@@ -77,7 +77,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2.3.4
+      - uses: actions/checkout@v3.0.2
 
       - uses: actions-rs/toolchain@v1.0.7
         with: