ci: 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](https://github.com/actions/upload-artifact/compare/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>

.github/workflows/build_docs.yml

@@ -91,7 +91,7 @@ jobs:
         run: cp ${{ env.RELEASE_VERSION }}/README.html docs/index.html
 
       - name: Upload README.html as an artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: README.html
           path: ${{ env.RELEASE_VERSION }}/README.html

.github/workflows/qemu-kvm-integration-tests.yml

@@ -211,7 +211,7 @@ jobs:
 
       - name: Upload test logs on failure
         if: failure()
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: "logs-${{ matrix.scenario.image }}-${{ matrix.scenario.env }}"
           path: |

.github/workflows/test_converting_readme.yml

@@ -40,7 +40,7 @@ jobs:
             --output README.html README.md
 
       - name: Upload README.html as an artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: README.html
           path: README.html