Bump actions/checkout from 5 to 6 (#259)

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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/docker_build.yml

@@ -13,6 +13,6 @@ jobs:
     docker_build:
         runs-on: ubuntu-latest
         steps:
-        -   uses: actions/checkout@v5
+        -   uses: actions/checkout@v6
         -   name: Build the Docker image
             run: make docker_build

.github/workflows/new_issue.yml

@@ -9,7 +9,7 @@ jobs:
         permissions:
             issues: write
         steps:
-        -   uses: actions/checkout@v5
+        -   uses: actions/checkout@v6
             with:
                 ref: main
         -   name: Install FAQtory

.github/workflows/package.yml

@@ -12,7 +12,7 @@ jobs:
     package:
         runs-on: ubuntu-latest
         steps:
-        -   uses: actions/checkout@v5
+        -   uses: actions/checkout@v6
             with:
                 submodules: recursive
                 fetch-depth: 0

.github/workflows/system_tests.yml

@@ -25,7 +25,7 @@ jobs:
             fail-fast: false
         steps:
         -   name: Clone repo
-            uses: actions/checkout@v5
+            uses: actions/checkout@v6
         -   name: Set up Python ${{ matrix.python-version }}
             uses: actions/setup-python@v6
             with:

.github/workflows/test_and_coverage.yml

@@ -24,7 +24,7 @@ jobs:
         steps:
 
         -   name: Clone repo
-            uses: actions/checkout@v5
+            uses: actions/checkout@v6
 
         -   name: Set up Python ${{ matrix.python-version }}
             uses: actions/setup-python@v6

.github/workflows/validate_cff.yml

@@ -18,7 +18,7 @@ jobs:
     validate_cff:
         runs-on: ubuntu-latest
         steps:
-        -   uses: actions/checkout@v5
+        -   uses: actions/checkout@v6
         -   name: Check whether the citation metadata from CITATION.cff is valid
             uses: citation-file-format/cffconvert-github-action@2.0.0
             with: