Update psalm/plugin-phpunit requirement from ^0.15.0 to ^0.16.1 (#85)

Updates the requirements on [psalm/plugin-phpunit](https://github.com/psalm/psalm-plugin-phpunit) to permit the latest version.
- [Release notes](https://github.com/psalm/psalm-plugin-phpunit/releases)
- [Commits](psalm/psalm-plugin-phpunit@0.15.0...0.16.1)

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

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composer.json

@@ -25,7 +25,7 @@
         "phpstan/phpstan-phpunit": "0.12.20",
         "phpstan/phpstan-strict-rules": "0.12.9",
         "phpunit/phpunit": "^9.2",
-        "psalm/plugin-phpunit": "^0.15.0",
+        "psalm/plugin-phpunit": "^0.16.1",
         "roave/infection-static-analysis-plugin": "^1.7",
         "thecodingmachine/phpstan-safe-rule": "^1.0",
         "vimeo/psalm": "^4.4"