Update GHA checkout action version

Author: blowekamp

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - name: Running Validate Content

.github/workflows/s3sync.yml

@@ -14,7 +14,7 @@ jobs:
     name: Sync simpleitk bucket
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Install dependencies
       run: |
         sudo apt-get update