tweak how installed file sizes are checked

.github/workflows/publish.yml

@@ -39,11 +39,14 @@ jobs:
     - name: Check metadata verification
       run: python -m twine check --strict dist/*
 
-    - name: Ensure that the wheel installs correctly, and show installed size
+    - name: Ensure that the wheel installs successfully
       run: |
-        pip install $(find dist -type f -name "*.whl")
-        du -h $(python -c "import pvlib; print(pvlib.__path__[0])")
-        
+        mkdir ./tmp
+        pip install $(find dist -type f -name "*.whl") --target=./tmp
+
+    - name: List installed file sizes
+        du -h ./tmp
+
     # only publish distribution to PyPI for tagged commits
     - name: Publish distribution to PyPI
       if: startsWith(github.ref, 'refs/tags/v')