Start testing PHP 8.6-alpha

Author: tvdijen

.github/workflows/php.yml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version: ['8.5']
+        php-version: ['8.5', '8.6']
 
     uses: simplesamlphp/simplesamlphp-test-framework/.github/workflows/reusable_phplinter.yml@v1
     secrets: inherit
@@ -47,7 +47,7 @@ jobs:
       fail-fast: false
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: ['8.5']
+        php-versions: ['8.5', '8.6']
 
     steps:
       - name: Setup PHP, with composer and extensions