fix(ci): corregir comilla duplicada en php-version del workflow

Author: Daniel Fernández Giménez

.github/workflows/tests.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version: [''8.1', '8.2', '8.3', '8.4']
+        php-version: ['8.1', '8.2', '8.3', '8.4']
         database: ['mysql', 'postgresql']
 
     env: