Bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  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/CI.yml

@@ -38,7 +38,7 @@ jobs:
           echo "isotag=${VER}-${REL}" >> $GITHUB_ENV
 
       - name: Upload iso artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: mbp-linuxmint-cinnamon-${{ steps.tag.outputs.tag }}.z01
           path: ${{ github.workspace }}/output/*
@@ -103,7 +103,7 @@ jobs:
           echo "isotag=${VER}-${REL}" >> $GITHUB_ENV
 
       - name: Upload iso artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: mbp-linuxmint-mate-${{ steps.tag.outputs.tag }}.z01
           path: ${{ github.workspace }}/output/*
@@ -163,7 +163,7 @@ jobs:
           echo "isotag=${VER}-${REL}" >> $GITHUB_ENV
 
       - name: Upload iso artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: mbp-linuxmint-xfce-${{ steps.tag.outputs.tag }}.z01
           path: ${{ github.workspace }}/output/*