Update main.yml

Don't run CI on pushes to devel (only pull requests).

.github/workflows/main.yml

@@ -7,13 +7,12 @@ on:
   push:
     branches:
       - "main"
-      - "devel"
   pull_request:
     branches:
       - "main"
       - "devel"
   schedule:
-    # Nightly tests run on master by default: (PSJ: this runs weekly on sunday)
+    # Nightly tests run on master by default:
     #   Scheduled workflows run on the latest commit on the default or base branch.
     #   (from https://help.github.com/en/actions/reference/events-that-trigger-workflows#scheduled-events-schedule)
     - cron: "0 0 * * 0"
@@ -24,7 +23,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ macOS-latest, ubuntu-latest, windows-latest ]
+        os: [ macOS-latest ]
         python-version: [ 3.7, 3.8, 3.9 ]
 
     steps: