Bump to actions/{upload,download}-artifact to v4

This update requires artifacts to be uniquely named, so to make things
easier for the last step we introduce a new intermediate merge step as
per the action's documentation.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

.github/workflows/deploy-to-pypi.yml

@@ -85,8 +85,9 @@ jobs:
           CIBW_TEST_COMMAND: "bash -c 'cd \"{project}\"; pytest -vv'"
           CIBW_TEST_REQUIRES: pytest cffi
 
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         with:
+          name: wheels-${{ matrix.os }}-${{ matrix.arch }}
           path: ./wheelhouse/*.whl
 
   build_sdist:
@@ -106,18 +107,28 @@ jobs:
       - name: Build sdist
         run: python setup.py sdist
 
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         with:
+          name: source-dist
           path: dist/*.tar.gz
 
+  merge_artifacts:
+    needs: [build_wheels, build_sdist]
+    runs-on: ubuntu-latest
+    steps:
+      - name: Merge Artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          name: all-artifacts
+
   upload_pypi:
     needs: [build_wheels, build_sdist]
     runs-on: ubuntu-latest
     if: startsWith(github.event.ref, 'refs/tags/v')
     steps:
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v4
         with:
-          name: artifact
+          name: all-artifacts
           path: dist
 
       - uses: pypa/gh-action-pypi-publish@master