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/release-debian.yml

@@ -23,7 +23,7 @@ jobs:
           apt-get -y upgrade
           apt-get -y install devscripts dpkg-dev debhelper equivs
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Bump version
         run: |
           export DEBEMAIL='[email protected]'

.github/workflows/test-debian.yml

@@ -18,7 +18,7 @@ jobs:
           apt-get -y upgrade
           apt-get -y install devscripts dpkg-dev debhelper equivs
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Bump version
         run: |
           export DEBEMAIL='[email protected]'