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/check-arduino.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Arduino Lint
         uses: arduino/arduino-lint-action@v2

.github/workflows/compile-examples.yml

@@ -93,7 +93,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Compile examples
         uses: arduino/compile-sketches@v1

.github/workflows/spell-check.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # See: https://github.com/codespell-project/actions-codespell/blob/master/README.md
       - name: Spell check

.github/workflows/sync-labels.yml

@@ -27,7 +27,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Download JSON schema for labels configuration file
         id: download-schema
@@ -105,7 +105,7 @@ jobs:
           echo "::set-output name=flag::--dry-run"
 
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Download configuration files artifact
         uses: actions/download-artifact@v6