MNT, CI: Use separate jobs for WASM wheel uploads

This PR separates out wheel builds and the wheel
uploads into separate jobs, where the GHA actions
are used to share artifacts between jobs. This is a
slight restructure of the job, and is intended so that
a new runner is assigned to the job for security
reasons.

[skip azp] [skip circle] [skip cirrus]

Author: agriyakhetarpal

.github/workflows/emscripten.yml

@@ -32,11 +32,11 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
-permissions:
-  contents: read  # to fetch code (actions/checkout)
 
 jobs:
   build-wasm-emscripten:
+    permissions:
+      contents: read  # to fetch code (actions/checkout)
     name: Build NumPy distribution for Pyodide
     runs-on: ubuntu-22.04
     # To enable this workflow on a fork, comment out:
@@ -57,14 +57,27 @@ jobs:
         with:
           name: cp312-pyodide_wasm32
           path: ./wheelhouse/*.whl
+          if-no-files-found: error
+
+  # Push to https://anaconda.org/scientific-python-nightly-wheels/numpy
+  # WARNING: this job will overwrite any existing WASM wheels.
+  upload-wheels:
+    name: Upload NumPy WASM wheels to Anaconda.org
+    runs-on: ubuntu-22.04
+    permissions: {}
+    needs: [build-wasm-emscripten]
+    if: >-
+      (github.repository == 'numpy/numpy') &&
+      (github.event_name == 'workflow_dispatch' && github.event.inputs.push_wheels == 'true') ||
+      (github.event_name == 'schedule')
+    steps:
+      - name: Download wheel artifact(s)
+        uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16  # v4.1.8
+        with:
+          path: wheelhouse/
+          merge-multiple: true
 
-        # Push to https://anaconda.org/scientific-python-nightly-wheels/numpy
-        # WARNING: this job will overwrite any existing WASM wheels.
       - name: Push to Anaconda PyPI index
-        if: >-
-          (github.repository == 'numpy/numpy') &&
-          (github.event_name == 'workflow_dispatch' && github.event.inputs.push_wheels == 'true') ||
-          (github.event_name == 'schedule')
         uses: scientific-python/upload-nightly-action@b67d7fcc0396e1128a474d1ab2b48aa94680f9fc  # v0.5.0
         with:
           artifacts_path: wheelhouse/