Run Test Workflow only if Go code was changed

Author: pofl

.github/workflows/echo.yml

@@ -4,9 +4,13 @@ on:
   push:
     branches:
       - master
+    paths:
+      - '**.go'
   pull_request:
     branches:
       - master
+    paths:
+      - '**.go'
 
 env:
   GO111MODULE: on