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)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [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/ExtendableFEMtest.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         with:
           version: '1'

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
           - os: macOS-14
             arch: x64
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
@@ -61,7 +61,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         with:
           version: '1'

.github/workflows/pre-commit-autoupdate.yml

@@ -13,7 +13,7 @@ jobs:
   auto-update:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
       - name: install pre-commit
         run: pip install pre-commit

.github/workflows/pre-commit.yml

@@ -8,7 +8,7 @@ jobs:
     name: run pre-commit
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - uses: julia-actions/setup-julia@v2
       with:
         version: 1