chore: change to run on macos instead of ubuntu

Author: cadenmyers13

.github/workflows/tests-on-pr.yml

@@ -14,7 +14,7 @@ jobs:
       run:
         shell: bash -l {0}
 
-    runs-on: ubuntu-latest
+    runs-on: macos-14
     steps:
       - name: Check out diffpy.srreal
         uses: actions/checkout@v4