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/build-linux.yml

@@ -65,7 +65,7 @@ jobs:
             build_octave: 0
             build_julia: 1
     steps:    
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Disable initramfs update
       run: sudo sed -i 's/yes/no/g' /etc/initramfs-tools/update-initramfs.conf
@@ -125,7 +125,7 @@ jobs:
 
     - name: Checkout CodSpeed integration library
       if: steps.cache-codspeed.outputs.cache-hit != 'true'
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         repository: CodSpeedHQ/codspeed-cpp
         ref: "${{ env.CODSPEED_VERSION }}"
@@ -266,7 +266,7 @@ jobs:
     runs-on: ubuntu-latest
     name: "distcheck"
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Disable initramfs update
       run: sudo sed -i 's/yes/no/g' /etc/initramfs-tools/update-initramfs.conf

.github/workflows/build-macos.yml

@@ -66,7 +66,7 @@ jobs:
             build_octave: 0
             build_julia: 1
     steps:    
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - uses: gerlero/brew-install@v1
       with:
@@ -124,7 +124,7 @@ jobs:
 
     # - name: Checkout CodSpeed integration library
     #   if: steps.cache-codspeed.outputs.cache-hit != 'true'
-    #   uses: actions/checkout@v5
+    #   uses: actions/checkout@v6
     #   with:
     #     repository: CodSpeedHQ/codspeed-cpp
     #     path: codspeed-cpp
@@ -247,7 +247,7 @@ jobs:
       CPPFLAGS: "-I/opt/homebrew/include"
       LDFLAGS: "-L/opt/homebrew/lib"
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - uses: gerlero/brew-install@v1
       with: