upgrade github actions, add dependabot for them

Author: syphar

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"

.github/workflows/main.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout the source code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Run the custom linter
         run: ./lint.sh
@@ -36,13 +36,13 @@ jobs:
 
     steps:
       - name: Checkout the source code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Build the Docker image
         run: docker build -t ghcr.io/${{ github.repository }}/${{ matrix.image }}:latest ${{ matrix.image }}/
 
       - name: Authenticate with GitHub Container Registry
-        uses: docker/login-action@v1
+        uses: docker/login-action@v2
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}