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] <support@github.com>

Author: dependabot[bot]

.github/workflows/gt-update.yml

@@ -66,7 +66,7 @@ jobs:
           	} && false || cd "$currentDir" && rm -r "$tmpDir" && "${result:-false}"
           # end install.doc.sh
       #gt-placeholder-gh-action-checkout-1-start
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       #gt-placeholder-gh-action-checkout-1-end
       - id: set-matrix
         run: |
@@ -114,7 +114,7 @@ jobs:
           	} && false || cd "$currentDir" && rm -r "$tmpDir" && "${result:-false}"
           # end install.doc.sh
       #gt-placeholder-gh-action-checkout-2-start
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       #gt-placeholder-gh-action-checkout-2-end
       - name: reset gpg keys
         run: gt reset --gpg-only true -r "${{ matrix.remote }}"
@@ -163,7 +163,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       #gt-placeholder-gh-action-checkout-3-start
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       #gt-placeholder-gh-action-checkout-3-end
       - name: check if signing key already are or will expire within the next 3 months
         run: |

.github/workflows/quality-assurance.yml

@@ -9,7 +9,7 @@ jobs:
     name: before-pr.sh
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: install shellcheck
         run: ./src/ci/install-shellcheck.sh