build(deps-dev): update infection/infection requirement (#26)

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@0.20.2...0.21.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

composer.json

@@ -20,7 +20,7 @@
     "require-dev": {
         "doctrine/coding-standard": "^8.2",
         "ergebnis/composer-normalize": "^2.13",
-        "infection/infection": "^0.20.2",
+        "infection/infection": "^0.21.0",
         "phpstan/extension-installer": "^1.1",
         "phpstan/phpstan": "^0.12.69",
         "phpstan/phpstan-phpunit": "^0.12.17",