Reformat test workflow

Use a pure YAML formatting style, rather than a mixture of YAML and JSON styles.

Author: per1234

.github/workflows/test.yml

@@ -1,6 +1,8 @@
 name: Test Action
 
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
 
 jobs:
   test:
@@ -11,7 +13,9 @@ jobs:
 
     strategy:
       matrix:
-        operating-system: [ubuntu-latest, windows-latest]
+        operating-system:
+          - ubuntu-latest
+          - windows-latest
 
     steps:
       - name: Checkout