build(deps): bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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/esphome-ci.yaml

@@ -10,7 +10,7 @@ jobs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
       - name: 📥 Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: 📄 Build matrix
         id: set-matrix
@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: 📥 Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: 🧪 Run Coverage Check
         env:
@@ -43,7 +43,7 @@ jobs:
 
     steps:
       - name: 📥 Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: 🔄 Update ref to current branch
         run: |