Make sure that there are no errors set for an input after it is signed.
This is useful for when there are multiple ScriptPubKeyMans. Some may
fail to sign, but one may be able to sign, and after it does, we don't
want there to be any more errors there.
Backport of Core PR18115 part [9/9] : https://github.com/bitcoin/bitcoin/pull/18115/commits/d2774c09cfcc6c5c967d40bb094eabc8c0bdb6bf