[backport#17261 5/13] Always try to sign for all pubkeys in multisig
Summary:
https://github.com/bitcoin/bitcoin/pull/17261/commits/501acb5538008d98abe79288b92040bc186b93f3
Depends on D7849
Partial backport of Core PR17261
Test Plan:
ninja all check check-functional
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D7850