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/CI.yml

@@ -62,7 +62,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Setup Fortran compiler
       uses: fortran-lang/setup-fortran@v1.8.0
@@ -275,7 +275,7 @@ jobs:
         gcc_v: [11,12,13]
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Download Artifacts
       id: download_windows_artifacts
@@ -392,7 +392,7 @@ jobs:
       env:
         DEPLOY_BRANCH: ${{ secrets.DEPLOY_BRANCH && contains(github.ref, secrets.DEPLOY_BRANCH) && 1 || 0 }}
 
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       if: ${{ github.event_name == 'push' }}
 
     - name: Download Artifacts

.github/workflows/docs.yml

@@ -6,7 +6,7 @@ jobs:
   build-and-deploy:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: actions/setup-python@v6
       with:
         python-version: '3.x'

.github/workflows/meta.yml

@@ -56,7 +56,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: (Ubuntu) setup gcc version
       if: contains(matrix.os,'ubuntu') 

.github/workflows/release.yml

@@ -17,7 +17,7 @@ jobs:
       FORMAT: ${{ matrix.format }}
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
 
@@ -44,7 +44,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
 
@@ -124,7 +124,7 @@ jobs:
       env:
         DEPLOY_BRANCH: ${{ secrets.DEPLOY_BRANCH && contains(github.ref, secrets.DEPLOY_BRANCH) && 1 || 0 }}
 
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       if: ${{ github.event_name == 'push' }}
 
     - name: Download Artifacts