TxnGroup.sign_with_private_key should raise an error if the address is not one of the senders

[fergalwalsh]

tinyman-py-sdk/tinyman/utils.py

Line 103 in 40ca553

def sign_with_private_key(self, address, private_key):

If the address is not one of the senders we should raise an error.
This has tripped up some people who were passing a different address to the one used to generate the transactions but didn't get any error.

PS. Don't be tempted to refactor this to require only a private key and derive the address from that - that won't work for rekeyed accounts.