Force PHP 8.0.2 platform and downgrade phpunit accordingly

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

Author: come-nc

tests/integration/composer.json

@@ -1,6 +1,6 @@
 {
   "require-dev": {
-    "phpunit/phpunit": "^10.5",
+    "phpunit/phpunit": "^9.6",
     "behat/behat": "^3.13",
     "guzzlehttp/guzzle": "^7.8"
   },
@@ -16,5 +16,10 @@
         "features/bootstrap/"
       ]
     }
+  },
+  "config": {
+    "platform": {
+      "php": "8.0.2"
+    }
   }
 }