Update macOS and Cygwin 5.1.x workflows to avoid double runs

Author: jmid

.github/workflows/cygwin-51x.yml

@@ -1,6 +1,11 @@
 name: Cygwin 5.1
 
-on: [push, pull_request, workflow_dispatch]
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
 
 jobs:
   build:

.github/workflows/macosx-51x.yml

@@ -1,6 +1,11 @@
 name: macOS 5.1
 
-on: [push, pull_request, workflow_dispatch]
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
 
 jobs:
   build: