Fix workflow

Author: Riimu

.github/workflows/main.yml

@@ -2,16 +2,16 @@ name: CI
 
 on:
   push:
-    branches: [ master ]
+    branches: [master]
   pull_request:
-    branches: [ master ]
+    branches: [master]
   workflow_dispatch:
 
 jobs:
   tests:
     strategy:
       matrix:
-        operating-system: ubuntu-latest
+        operating-system: [ubuntu-latest]
         php-versions: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
     runs-on: ${{ matrix.operating-system }}
     steps:
@@ -36,4 +36,4 @@ jobs:
       - name: Setup problem matchers for PHPUnit
         run: echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
       - name: Test with phpunit
-        run: vendor/bin/phpunit
+        run: vendor/bin/phpunit