Update phpunit/phpunit requirement from ^10 to ^11

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/11.3.5/ChangeLog-11.3.md)
- [Commits](sebastianbergmann/phpunit@10.0.0...11.3.5)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

composer.json

@@ -10,7 +10,7 @@
     "ext-json": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "^10",
+    "phpunit/phpunit": "^11",
     "brain/monkey": "^2.6",
     "phpstan/phpstan": "^1.11",
     "szepeviktor/phpstan-wordpress": "^1.3",