Fix flaky tests on src/validations/theme.test.ts

[karreiro]

The tests were a bit flaky due to a race condition in the beforeEach setup. The code used forEach with async operations to create test directories, but forEach doesn't wait for async functions to complete.

That caused a race between directory creation and test execution, leading to ENOENT errors when tests tried to write files before directories existed.

The fix involved replacing forEach with Promise.all() to ensure all directory creation operations are completed before test execution begins. This change eliminates the timing-dependent behavior that caused the intermittent failures.

Before:

After: