Add nightly CI run (#125)

.circleci/config.yml

@@ -222,10 +222,7 @@ jobs:
       - <<: *run-tox-step
       - <<: *save-cache-step
 
-workflows:
-  version: 2
-  test:
-    jobs:
+define: &all_jobs
   - docs
   - py38-core
   - py39-core
@@ -244,3 +241,18 @@ workflows:
   - py312-wheel
   - py311-windows-wheel
   - py312-windows-wheel
+
+workflows:
+  version: 2
+  test:
+    jobs: *all_jobs
+  nightly:
+    triggers:
+      - schedule:
+          # Weekdays 12:00p UTC
+          cron: "0 12 * * 1,2,3,4,5"
+          filters:
+            branches:
+              only:
+                - main
+    jobs: *all_jobs