fix: Update IsPostalCode.ts, optional ' locale ' causing errors in runtime

[csori99]

Locale should not be marked as optional, under the hood it doesnt accept undefined as a value, causing errors.

Description

Locale should not be marked as optional, under the hood it doesnt accept undefined as a value, causing errors.

Checklist

• the pull request title describes what this PR does (not a vague title like Update index.md)
• the pull request targets the default branch of the repository (develop)
• the code follows the established code style of the repository
  • npm run prettier:check passes
  • npm run lint:check passes
• tests are added for the changes I made (if any source code was modified)
• documentation added or updated
• I have run the project locally and verified that there are no errors

Fixes

fixes #[issue number], fixes #[issue number]