Add testing on the newest PHP 8.1 to the CI config (#465)

Author: bocharsky-bw

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: [ '7.2', '7.3', '7.4', '8.0' ]
+        php: [ '7.2', '7.3', '7.4', '8.0', '8.1' ]
         strategy: [ 'highest' ]
         sf_version: ['']
         include:
@@ -43,4 +43,3 @@ jobs:
 
       - name: Run tests
         run: ./vendor/bin/simple-phpunit
-