Update phpunit/phpunit requirement from ^5.7.21 || ^6.5 || ^7.5 || ^8 to ^11.2.6

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

composer.json

@@ -17,7 +17,7 @@
     "installer-name": "nodeinfo"
   },
   "require-dev": {
-    "phpunit/phpunit": "^5.7.21 || ^6.5 || ^7.5 || ^8",
+    "phpunit/phpunit": "^11.2.6",
     "phpcompatibility/php-compatibility": "*",
     "phpcompatibility/phpcompatibility-wp": "*",
     "squizlabs/php_codesniffer": "3.*",