build: added PHP 7.4

.github/workflows/blank.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php: [7.1, 7.2, 7.3]
+        php: [7.1, 7.2, 7.3, 7.4]
     steps:
     - uses: actions/checkout@v1
     - name: Debug if needed