#4618 Add tests for checking shareable public key

[martgil]

This PR adds a tests for checking shareable public key on my_keys.htm on FlowCrypt Settings -> Public Key.

close #4618

---

Tests (delete all except exactly one):

• Tests added or updated

---

To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[martgil]

Hello @sosnovsky - this one is ready for a review. thank you!

[sosnovsky]

well done 👍