build(deps): 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/coreboot-example.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: 'recursive'
 

.github/workflows/linuxboot-example-separate-jobs.yml

@@ -17,7 +17,7 @@ jobs:
       artifact-name-RELEASE: ${{ steps.firmware-action.outputs.artifact-name }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: 'recursive'
 
@@ -48,7 +48,7 @@ jobs:
       artifact-name-RELEASE: ${{ steps.firmware-action.outputs.artifact-name }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: 'recursive'
 
@@ -74,7 +74,7 @@ jobs:
         release_type: ['DEBUG', 'RELEASE']
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: 'recursive'
       - name: Fetch few missing submodules

.github/workflows/linuxboot-example.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: 'recursive'
       - name: Fetch few missing submodules