Bump actions/checkout from 2 to 4 (#6)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [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/v2...v4)

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

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

.github/workflows/ci.yml

@@ -27,12 +27,12 @@ jobs:
         uses: actions/setup-python@v2
 
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           path: extension
 
       - name: Checkout SourceMod
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           repository: alliedmodders/sourcemod
           ref: ${{ matrix.sourcemod-version }}
@@ -40,13 +40,13 @@ jobs:
           submodules: recursive
 
       - name: Checkout AMBuild
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           repository: alliedmodders/ambuild
           path: ambuild
 
       - name: Checkout sm-ext-common
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           repository: srcdslab/sm-ext-common
           path: sourcemod/extensions/sm-ext-common