Build: Bump actions/download-artifact from 4 to 7

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 7.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v7)

---
updated-dependencies:
- dependency-name: actions/download-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/python-ci.yml

@@ -193,7 +193,7 @@ jobs:
     - name: Install dependencies
       run: uv sync --group dev
     - name: Download all coverage artifacts
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v7
       with:
         pattern: coverage-*
         merge-multiple: true