fix: bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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] <support@github.com>

Author: dependabot[bot]

.github/workflows/client-generate.yml

@@ -17,7 +17,7 @@ jobs:
   lint:
      runs-on: ubuntu-latest
      steps:
-     - uses: actions/checkout@v4
+     - uses: actions/checkout@v6
      - run: npm i -g @redocly/cli@latest
      - run: redocly lint openapi.json
 
@@ -29,7 +29,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Setup PHP with PECL extension
       uses: shivammathur/setup-php@v2

.github/workflows/php.yml

@@ -17,7 +17,7 @@ jobs:
   lint:
      runs-on: ubuntu-latest
      steps:
-     - uses: actions/checkout@v4
+     - uses: actions/checkout@v6
      - run: npm i -g @redocly/cli@latest
      - run: redocly lint openapi.json
      - name: Run php-cs-fixer
@@ -29,7 +29,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Setup PHP with PECL extension
       uses: shivammathur/setup-php@v2