Fix internal server error when updating 3pid address with invalid email (#18125)

When updating 3pid for a user email from admin api and sending invalid
email the server throws 500 internal server error.
changed to 400 Bad request and returned the error message

Signed-off-by: qashlan <ahmedelqashlan@gmail.com>
Signed-off-by: Ahmed Qashlan <ahmedelqashlan@gmail.com>