Fix upload artefacts steps in GH Actions workflows

Version 4 of 'actions/download-artifact' introduced a breaking change
which broke the 'build-wheels' job.

See actions/upload-artifact#478.

.github/workflows/test_and_publish.yml

@@ -81,7 +81,7 @@ jobs:
       - name: Upload artefacts to GitHub
         uses: actions/upload-artifact@v4
         with:
-          name: dist-packages
+          name: cibw-wheels-${{ matrix.os }}-${{ strategy.job-index }}
           path: wheelhouse/*.whl
 
   build-sdist:
@@ -112,7 +112,7 @@ jobs:
       - name: Upload artefacts to GitHub
         uses: actions/upload-artifact@v4
         with:
-          name: dist-packages
+          name: cibw-sdist
           path: dist/*.tar.gz
 
   publish-to-test-pypi:
@@ -129,8 +129,9 @@ jobs:
       - name: Download artefacts
         uses: actions/download-artifact@v4
         with:
-          name: dist-packages
+          name: cibw-*
           path: dist
+          merge-multiple: true
 
       - name: Publish to TestPyPI
         uses: pypa/gh-action-pypi-publish@v1.8.14
@@ -153,8 +154,9 @@ jobs:
       - name: Download artefacts
         uses: actions/download-artifact@v4
         with:
-          name: dist-packages
+          name: cibw-*
           path: dist
+          merge-multiple: true
 
       - name: Publish to test PyPI
         uses: pypa/gh-action-pypi-publish@v1.8.14