Update actions/checkout action to v3 (#8)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/auto-readme.yml

@@ -24,7 +24,7 @@ jobs:
   update:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Find default branch name
         id: defaultBranch

.github/workflows/validate-codeowners.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: "Checkout source code at current commit"
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       # Leave pinned at 0.7.1 until https://github.com/mszostok/codeowners-validator/issues/173 is resolved
     - uses: mszostok/codeowners-validator@v0.7.1
       if: github.event.pull_request.head.repo.full_name == github.repository