fix(phpstan): correct variable type

Related: #4 (closed)

.phive/phars.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<phive xmlns="https://phar.io/phive">
+  <phar name="phpstan" version="1.11.8" installed="1.11.8" location="./tools/phpstan" copy="false"/>
+  <phar name="phpunit" version="^10.5.20" installed="10.5.20" location="./tools/phpunit" copy="false"/>
+  <phar name="phpcs" version="^3.10.1" installed="3.10.1" location="./tools/phpcs" copy="false"/>
+  <phar name="phpcbf" version="^3.10.1" installed="3.10.1" location="./tools/phpcbf" copy="false"/>
+  <phar name="captainhook" version="^5.23.3" installed="5.23.3" location="./tools/captainhook" copy="false"/>
+</phive>