[GitHubEnterprise-3.15] Update dependency wyrihaximus/async-test-utilities to v8

Author: renovate[bot]

clients/GitHubEnterprise-3.15/composer.json

@@ -21,7 +21,7 @@
     "wyrihaximus/react-awaitable-observable": "^1.0"
   },
   "require-dev": {
-    "wyrihaximus/async-test-utilities": "^7.0.3"
+    "wyrihaximus/async-test-utilities": "^7.0.3 || ^8.0.0"
   },
   "autoload": {
     "psr-4": {