Bump actions/checkout from 5 to 6 (#1281)

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [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/v5...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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/check_urls.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Restore lychee cache
         uses: actions/cache@v4

.github/workflows/export_web.yml

@@ -16,7 +16,7 @@ jobs:
       image: barichello/godot-ci:4.3
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup
         run: |

.github/workflows/static_checks.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Install dependencies
         run: |