build(deps-dev): update infection/infection requirement

Updates the requirements on [infection/infection](https://github.com/infection/infection) to permit the latest version.
- [Release notes](https://github.com/infection/infection/releases)
- [Changelog](https://github.com/infection/infection/blob/master/CHANGELOG.md)
- [Commits](infection/infection@0.17.5...0.21.5)

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

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

composer.json

@@ -20,7 +20,7 @@
     },
     "require-dev": {
         "composer/composer": "1.10.10",
-        "infection/infection": "^0.17.5",
+        "infection/infection": "^0.21.5",
         "mikey179/vfsstream": "^1.6",
         "phpro/grumphp": "^0.17.1 || ^0.19.0 || ^0.20.0",
         "phpstan/phpstan": "^1.2.0",