Update GitHub Actions to use checkout@v4

Author: Antynea

.github/workflows/bump-version-on-merge.yml

@@ -15,19 +15,20 @@ jobs:
     if: github.actor != 'github-actions[bot]'
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           ref: master
 
       - name: Update version in config
         run: |
-          version="$(git rev-parse --abbrev-ref HEAD)-$(date -u -Iseconds)"
+          version="master-$(date -u -Iseconds)"
           sed -i "s/GRUB_BTRFS_VERSION=.*/GRUB_BTRFS_VERSION=${version}/" config
+          echo "VERSION=${version}" >> $GITHUB_ENV
 
       - name: Commit updated config
         run: |
           git config user.name "github-actions[bot]"
           git config user.email "github-actions[bot]@users.noreply.github.com"
           git add config
-          git commit -m "chore: bump version to ${version}"
+          git commit -m "chore: bump version to ${{ env.VERSION }}"
           git push origin master