Update master php testing versions

Signed-off-by: Joas Schilling <coding@schilljs.com>

Author: nickvergessen

.github/workflows/lint.yml

@@ -13,7 +13,7 @@ jobs:
 
     strategy:
       matrix:
-        php-versions: ['7.4', '8.0']
+        php-versions: ['7.4', '8.0', "8.1"]
 
     name: php${{ matrix.php-versions }}
     steps:

.github/workflows/phpunit.yml

@@ -18,7 +18,7 @@ jobs:
       # do not stop on another job's failure
       fail-fast: false
       matrix:
-        php-versions: ['7.4', '8.0']
+        php-versions: ['7.4', '8.0', "8.1"]
         databases: ['sqlite']
         server-versions: ['master']