attempt to get back to just 1 artifact [wheel build]

Author: Shane Snyder

.github/workflows/build_wheels.yml

@@ -61,3 +61,13 @@ jobs:
         with:
           name: pydarshan-wheels-${{ matrix.os }}
           path: ./wheelhouse/*.whl
+          retention-days: 0
+
+  merge_artifacts:
+    name: Merge built wheel artifacts
+    needs: build_wheels
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/upload-artifact/merge@v4
+        with:
+          name: pydarshan-wheels-all