Update phpstan/phpstan requirement from 1.11.9 to 1.12.5 (#299)

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/2.0.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.11.9...1.12.5)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-type: direct:development
...

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

composer.json

@@ -29,7 +29,7 @@
     "require-dev": {
         "phpunit/phpunit": "^9.0 || ^10.0",
         "friendsofphp/php-cs-fixer": "^3.5",
-        "phpstan/phpstan": "1.11.9"
+        "phpstan/phpstan": "1.12.5"
     },
     "autoload": {
         "psr-4": { "Conekta\\" : "lib/" }