Restrict push trigger to master branch

Author: Crown421

.github/workflows/main.yml

@@ -1,7 +1,9 @@
 name: julia 1.0/1.3
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   testMKLjl:

.github/workflows/nightly.yml

@@ -1,6 +1,8 @@
 name: julia nightly
 on:
   push:
+    branches:
+      - master
   pull_request:
   schedule:
     - cron:  '1 0 1,15 * *'