Re-add max parallel so we don't hit ngrok rate limits.

Author: alexdlaird

.github/workflows/build.yml

@@ -26,6 +26,7 @@ jobs:
 
     strategy:
       fail-fast: false
+      max-parallel: 3
       matrix:
         os: [ ubuntu-latest, macos-latest, windows-latest ]
         python-version: [ "3.12" ]