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] <[email protected]>

Author: dependabot[bot]

.github/workflows/build-ci.yaml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - name: Pull Yaru
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Check sources structure
       run: |

.github/workflows/build-deb.yaml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Checkout Yaru code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Build debian packages and sources
         uses: canonical/desktop-engineering/gh-actions/common/build-debian@main

.github/workflows/open-pr-on-changes.yaml

@@ -83,7 +83,7 @@ jobs:
       ]
     steps:
       # Checkout code
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Download from ${{ matrix.buildenv.repo }}, on branch ${{ matrix.buildenv.upstreambranch }}
         id: checknewupstream
         run: |

.github/workflows/open-pr-on-icons-changes.yaml

@@ -174,7 +174,7 @@ jobs:
       ]
     steps:
       # Checkout code
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Download from ${{ matrix.buildenv.repo }}, on branch ${{ matrix.buildenv.upstreambranch }}
         id: checknewupstream
         run: |

.github/workflows/open-pr-on-optimized-symbolic-icons-changes.yaml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Yaru code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup common variables
         id: env

.github/workflows/open-pr-on-rendered-icons-changed.yaml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Yaru code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
           persist-credentials: true

.github/workflows/track-lp-issues.yaml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
       # Checkout code
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install Python 3
         uses: actions/[email protected]
       - uses: canonical/desktop-engineering/gh-actions/common/dpkg-install-speedup@main