Add test triggering the second carry in secp384r1

[yanesca]

Suggested enhancement

Triggering the second carry in mbedtls_ecp_mod_p384_raw() might or might not be possible. If it is possible, we need to add a test to trigger this case, if it is not, we need to record the proof in git history it and remove the unused code.

Neither of these tasks are trivial. After some preliminary investigation it seems likely that such case exists.

Justification

Mbed TLS needs this to complete the test coverage of this function or alternatively remove the unnecessary code and save some code size.

[yanesca]

Closing it as resolved: #7222 (comment)