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)
- [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/presubmit.yaml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: checkout
-        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
       - name: build
         run: ./tool/github.sh
   checker:
@@ -31,7 +31,7 @@ jobs:
         bot: [CHECK_BOT, DART_BOT, UNIT_TEST_BOT, VERIFY_BOT]
     steps:
       - name: checkout
-        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
       - name: Linux ${{ matrix.bot }}
         run: ./tool/github.sh
         env:

.github/workflows/update_flutter.yaml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           token: ${{ secrets.FLUTTERACTIONSBOT_CP_TOKEN }}