Bump actions/checkout from 2 to 4

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](actions/checkout@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]>

.github/workflows/docker.yml

@@ -7,7 +7,7 @@ jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Build Docker Image
         run: |
           docker build -t vmaf .

.github/workflows/ffmpeg.yml

@@ -41,7 +41,7 @@ jobs:
         if: matrix.os == 'macos-10.15'
         run: |
           brew install -q ninja nasm
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Build vmaf
         run: |
           meson setup libvmaf libvmaf/build --buildtype release

.github/workflows/libvmaf.yml

@@ -65,7 +65,7 @@ jobs:
           meson --version
           ccache --version
 
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Run meson
         run: |
           meson setup libvmaf libvmaf/build --buildtype release --prefix $PWD/install -Denable_float=true

.github/workflows/windows.yml

@@ -26,7 +26,7 @@ jobs:
       run:
         shell: msys2 {0}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Cache ccache files