GH Actions: improve readability of the job title

When the PHP version nr is provided as a string, the full text will show in the `title`, otherwise, for PHP 8.0, it would be cut off to `8` (float to integer cast).

Author: jrfnl

.github/workflows/run-tests.yml

@@ -21,7 +21,7 @@ jobs:
 
     strategy:
       matrix:
-        php: [8.0, 7.4, 7.3]
+        php: ['8.0', '7.4', '7.3']
         dependency-version: [prefer-lowest, prefer-stable]
         experimental: [false]