Bump actions/checkout from 2 to 3 (#37)

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/CI.yml

@@ -18,7 +18,7 @@ jobs:
             fail-fast: false
 
         steps:
-            - uses: actions/checkout@v2
+            - uses: actions/checkout@v3
 
             - name: Setup PHP
               uses: shivammathur/setup-php@v2

.github/workflows/phpCS.yml

@@ -7,7 +7,7 @@ jobs:
         name: PHP CodeSniffer
         runs-on: ubuntu-latest
         steps:
-            - uses: actions/checkout@v2
+            - uses: actions/checkout@v3
 
             - name: Setup PHP
               uses: shivammathur/setup-php@v2