Bump actions/checkout from 2 to 3 (paritytech#11463)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v3)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/check-labels.yml

@@ -8,7 +8,7 @@ jobs:
   check-labels:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 0
           ref: ${{ github.event.pull_request.head.ref }}

.github/workflows/md-link-check.yml

@@ -12,7 +12,7 @@ jobs:
   markdown-link-check:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - uses: gaurav-nelson/github-action-markdown-link-check@7481451f70251762f149d69596e3e276ebf2b236
       with:
         use-quiet-mode: 'yes'

.github/workflows/monthly-tag.yml

@@ -16,7 +16,7 @@ jobs:
           echo "::set-output name=new::$(date +'monthly-%Y-%m')"
           echo "::set-output name=old::$(date -d'1 month ago' +'monthly-%Y-%m')"
       - name: Checkout branch "master"
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           ref: 'master'
           fetch-depth: 0