Bump actions/checkout from 5 to 6

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](actions/checkout@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]>

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -14,17 +14,17 @@ jobs:
   check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
           override: true
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           repository: gtk-rs/gir
           ref: main
           path: gir
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           repository: gtk-rs/gtk4-rs
           ref: main

.github/workflows/regenerate_scheduled.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
       - name: Redownload, regenerate, reformat