ci: restrict GHA workflow triggers on push

Author: calebcartwright

.github/workflows/integration.yml

@@ -1,5 +1,9 @@
 name: integration
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   integration-tests:

.github/workflows/linux.yml

@@ -1,5 +1,9 @@
 name: linux
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   test:

.github/workflows/mac.yml

@@ -1,5 +1,9 @@
 name: mac
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   test:

.github/workflows/windows.yml

@@ -1,5 +1,9 @@
 name: windows
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   test: