[qt] Replaces numbered place marker %2 with %1.

Summary:
This PR closes #12015 in which @chen610620 suggests to replace numbered place marker %2 with %1.

Backport of Bitcoin Core PR12092
https://github.com/bitcoin/bitcoin/pull/12092

Test Plan:

make
./src/qt/bitcoin-qt -regtest

1. Open the "Send" dialog.
2. Enter a BCH testnet address.
3. Enter a valid amount.
4. Press "Send" button, at bottom.
5. Check that the confirmation message is Ok.

Reviewers: Fabien, #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4077