Update nette/tester requirement from 2.3.5 to 2.4.0

Updates the requirements on nette/tester to permit the latest version.

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

composer.json

@@ -20,7 +20,7 @@
         "texy/texy": "^3.1.3@dev"
     },
     "require-dev": {
-        "nette/tester": "2.3.5",
+        "nette/tester": "2.4.0",
         "phpstan/phpstan": "0.12.80",
         "phpstan/phpstan-strict-rules": "0.12.9",
         "pepakriz/phpstan-exception-rules": "0.11.6",