Bump actions/checkout from v1 to v2.3.3 (#2052)

Bumps [actions/checkout](https://github.com/actions/checkout) from v1 to v2.3.3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v1...a81bbbf8298c0fa03ea29cdc473d45769f953675)

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

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

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
       fail-fast: false
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2.3.3
         with:
           submodules: true
 

.github/workflows/check-formatting.yml

@@ -14,7 +14,7 @@ jobs:
       image: ubuntu:19.10
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2.3.3
     - name: apt-get update
       run: apt-get update