build(deps-dev): update laravel/cashier requirement from ^14.12 to ^15.0

Updates the requirements on [laravel/cashier](https://github.com/laravel/cashier-stripe) to permit the latest version.
- [Release notes](https://github.com/laravel/cashier-stripe/releases)
- [Changelog](https://github.com/laravel/cashier-stripe/blob/15.x/CHANGELOG.md)
- [Commits](laravel/cashier-stripe@v14.12.0...v15.0.0)

---
updated-dependencies:
- dependency-name: laravel/cashier
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -36,7 +36,7 @@
     "cknow/laravel-money": "^7.1",
     "ergebnis/phpstan-rules": "^1.0",
     "infection/infection": "~0.27",
-    "laravel/cashier": "^14.12",
+    "laravel/cashier": "^15.0",
     "nunomaduro/collision": "^7.7",
     "nunomaduro/larastan": "^2.6",
     "orchestra/testbench": "^8.5",