Merge #9350: [Trivial] Adding label for amount inside of tx_valid/tx_invalid.json

Summary:
988ce2d Adding 'amount' label to tx_valid/tx_invalid.json files (Chris Stewart)

Tree-SHA512: 11c216c6565ecaa5ff4eb6122f87d3b28f89db52d1e473c0678f61c240e133698adb05e717bfb9d3db36409dfb230b902dca4029a58633be36c9f85e0db3d973

Backport of Core PR9350

https://github.com/bitcoin/bitcoin/pull/9350/files

Test Plan: make check

Reviewers: #bitcoin_abc, deadalnix, Fabien, markblundeberg

Reviewed By: #bitcoin_abc, Fabien, markblundeberg

Subscribers: Fabien, markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D3279