BLD: Upload sdist artifact from CI

Now it is possible to inspect the sdist that is built, to
see what was included and
for debugging.

Inspired by needing to see what was acutally included in the sdist at
pandas-dev#46271

Author: NickCrews

.github/workflows/sdist.yml

@@ -54,6 +54,12 @@ jobs:
         pip list
         python setup.py sdist --formats=gztar
 
+    - name: Upload sdist artifact
+      uses: actions/upload-artifact@v3
+      with:
+        name: ${{ github.ref }}-${{matrix.python-version}}-sdist.gz
+        path: dist/*.gz
+
     - uses: conda-incubator/setup-miniconda@v2
       with:
         activate-environment: pandas-sdist