Update phpstan/phpstan requirement from ^0.12.55 to ^0.12.78

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Commits](phpstan/phpstan@0.12.55...0.12.78)

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -23,7 +23,7 @@
     "require-dev": {
         "nette/tester": "^2.3.5",
         "mockery/mockery": "^1.4.2",
-        "phpstan/phpstan": "^0.12.55",
+        "phpstan/phpstan": "^0.12.78",
         "phpstan/phpstan-strict-rules": "^0.12.9",
         "pepakriz/phpstan-exception-rules": "^0.11.2",
         "phpstan/phpstan-nette": "^0.12.10",