Move all checkout@v2 users to v3. (#20315)

.github/workflows/build.yml

@@ -165,7 +165,7 @@ jobs:
       matrix:
         arch: [amd64]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: hashicorp/actions-docker-build@v1
         with:
           version: ${{ needs.product-metadata.outputs.vault-version }}

.github/workflows/changelog-checker.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           ref: ${{ github.event.pull_request.head.sha }}
           fetch-depth: 0 # by default the checkout action doesn't checkout all branches

.github/workflows/milestone-checker.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Actions
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           repository: "grafana/grafana-github-actions"
           path: ./actions

.github/workflows/stable-website.yaml

@@ -10,7 +10,7 @@ jobs:
     name: Cherry pick to stable-website branch
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       with:
         ref: stable-website
     - run: |