ci: update actions/{upload,download}-artifact

See: https://github.com/actions/upload-artifact/blob/main/docs/MIGRATION.md#multiple-uploads-to-the-same-named-artifact
Closes: #873
Closes: #1005

.github/workflows/tests.yml

@@ -82,14 +82,14 @@ jobs:
 
       - name: Upload coverage data
         if: always() && matrix.session == 'tests'
-        uses: "actions/upload-artifact@v3"
+        uses: "actions/upload-artifact@v4.3.3"
         with:
-          name: coverage-data
+          name: "coverage-data-${{ matrix.python-version }}-${{ matrix.runs-on || 'ubuntu-latest' }}"
           path: ".coverage.*"
 
       - name: Upload documentation
         if: matrix.session == 'docs'
-        uses: "actions/upload-artifact@v3"
+        uses: "actions/upload-artifact@v4.3.3"
         with:
           name: docs
           path: "docs/_build"
@@ -119,9 +119,10 @@ jobs:
           pip install --constraint=.github/workflows/constraints.txt nox nox-poetry
           nox --version
       - name: Download coverage data
-        uses: actions/download-artifact@v3.0.2
+        uses: actions/download-artifact@v4.1.7
         with:
-          name: coverage-data
+          pattern: coverage-data-*
+          merge-multiple: true
 
       - name: Combine coverage data and display human readable report
         run: |