Bump actions/upload-artifact from 4 to 6 (#137)

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/plugin-package.yml

@@ -62,7 +62,7 @@ jobs:
 
       - name: Upload artifact
         id: upload-artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         if: ${{ ! startsWith(github.ref, 'refs/tags/') }}
         with:
           name: oqtopus_dev

.github/workflows/python-wheel-package.yml

@@ -42,7 +42,7 @@ jobs:
         run: python -m build
 
       - name: Upload wheel artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: oqtopus-wheel
           path: dist/*