fix: isISO31661Alpha2 currently allowing lowercase characters (#2629)

[cherites0610]

Description

Added a strict uppercase check in isISO31661Alpha2 before delegating to validator.js. This prevents lowercase characters from bypassing the validation. Also added a test case in IsISO31661Alpha2.spec.ts to ensure lowercase values are correctly rejected.

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 #2629