Bump actions/upload-artifact from 6 to 7

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 6 to 7.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v6...v7)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/testsite.yml

@@ -19,12 +19,12 @@ jobs:
       - name: Save PR number
         run: echo ${{ github.event.number }} > pr-number.txt
       - name: Upload PR number
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
           name: pr-number
           path: pr-number.txt
       - name: Archive generated site
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
             name: generated-site
             path: ./target/roq/