Try with older mpi4py.

.github/workflows/windows.yml

@@ -1,9 +1,9 @@
 name: Windows build
 
 on:
-  # push:
-  #   branches:
-  #     - main
+  push:
+    branches:
+      - "**"
   #   tags:
   #     - "v*"
   # pull_request:
@@ -98,7 +98,7 @@ jobs:
           (Get-Content __init__.py).Replace('# WINDOWSDLL', 'import os; os.add_dll_directory("D:/a/dolfinx/dolfinx-install/bin"); os.add_dll_directory("C:/Program Files (x86)/Intel/oneAPI/mpi/2021.12/opt/mpi/libfabric/bin")') | Set-Content __init__.py
           Get-Content __init__.py
 
-      - uses: mpi4py/setup-mpi@v1.2.6
+      - uses: mpi4py/setup-mpi@v1.2.2
         with:
           mpi: "intelmpi"
 
@@ -130,7 +130,7 @@ jobs:
       - name: Install build dependencies
         working-directory: dolfinx
         run: |
-          pip -v install --no-binary mpi4py -r python/build-requirements.txt
+          pip -v install --no-binary mpi4py -r "mpi4py<4"
 
       - name: Install DOLFINx (Python)
         working-directory: dolfinx