[DEPS][GHA]: Bump actions/checkout from 2 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -16,7 +16,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         name: Checkout
       - uses: actions/setup-dotnet@v4
         name: Setup

.github/workflows/packages.yml

@@ -36,7 +36,7 @@ jobs:
             target_repo: "wp-feature-flags"
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with: 
           fetch-depth: 0
           token: ${{ secrets.BOXUK_WP_ROBOT_ACCESS_TOKEN }}

.github/workflows/publish-npm.yml

@@ -18,7 +18,7 @@ jobs:
           - local_path: "feature-flags"
             target: "@boxuk/wp-feature-flags"
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with: 
           fetch-depth: 0
           token: ${{ secrets.BOXUK_WP_ROBOT_ACCESS_TOKEN }}

.github/workflows/test-php.yml

@@ -32,7 +32,7 @@ jobs:
     name: Test PHP ${{ matrix.php }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         if: github.event_name != 'workflow_run'
 
       - name: Checkout

.github/workflows/tests-js.yml

@@ -27,7 +27,7 @@ jobs:
     name: Test JS
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         if: github.event_name != 'workflow_run'
 
       - name: Checkout

.github/workflows/wordpress-deps.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
       # Setup
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
           persist-credentials: false