ci: update versions of GitHub actions used in CI

Author: striezel

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       # Checks-out the repository under $GITHUB_WORKSPACE.
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: 'recursive'
       - name: Install Debian packages
@@ -32,7 +32,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       # Checks-out the repository under $GITHUB_WORKSPACE.
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           submodules: 'recursive'
       - name: Install Debian packages