Revert to run only on master branch

Author: yizshi

.github/workflows/net-ci.yml

@@ -3,7 +3,7 @@ name: .NET CI
 on:
   push:
     branches:
-      - "*"
+      - master
   pull_request:
     branches:
       - master
@@ -53,4 +53,4 @@ jobs:
         run: msbuild.exe duo_api_csharp.sln
 
       - name: Run Tests dll
-        run: vstest.console.exe .\test\bin\Debug\test.dll
+        run: vstest.console.exe .\test\bin\Debug\test.dll