Update psalm/plugin-phpunit requirement from 0.15.1 to 0.16.1 (#101)

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@0.15.1...0.16.1)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

composer.json

@@ -40,7 +40,7 @@
         "phpstan/phpstan-phpunit": "0.12.18",
         "phpstan/phpstan-strict-rules": "0.12.9",
         "phpunit/phpunit": "^9.4",
-        "psalm/plugin-phpunit": "0.15.1",
+        "psalm/plugin-phpunit": "0.16.1",
         "roave/infection-static-analysis-plugin": "^1.6",
         "thecodingmachine/phpstan-safe-rule": "^1.0",
         "vimeo/psalm": "4.8.1"