build(deps-dev): update phpstan/phpstan-strict-rules requirement

Updates the requirements on [phpstan/phpstan-strict-rules](https://github.com/phpstan/phpstan-strict-rules) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan-strict-rules/releases)
- [Commits](phpstan/phpstan-strict-rules@1.5.2...1.6.1)

---
updated-dependencies:
- dependency-name: phpstan/phpstan-strict-rules
  dependency-type: direct:development
...

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

composer.json

@@ -27,7 +27,7 @@
 		"phpstan/extension-installer": "1.4.3",
 		"phpstan/phpstan": "1.12.6",
 		"phpstan/phpstan-deprecation-rules": "1.1.4",
-		"phpstan/phpstan-strict-rules": "1.5.2",
+		"phpstan/phpstan-strict-rules": "1.6.1",
 		"symfony/config": "~4.4 || ~5.0",
 		"symfony/dependency-injection": "~4.4 || ~5.0",
 		"symfony/http-kernel": "~4.4 || ~5.0",