Quote floats so they appear as strings in GitHub Actions

Not really important with 8.1+ but one day, there will be PHP 9.0.

Author: spaze

.github/workflows/php.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         php-version:
-          - 8.1
+          - "8.1"
 
     steps:
     - uses: actions/checkout@v2