bug: resolve keyring flag properly

[dudong2]

Description

ref. cosmos/cosmos-sdk#19060

Closes: #87

how to test

• test command cantod tx feegrant prune --from <addr> --gas-prices 10000000000000000acanto --home <home dir> --chain-id canto_7700-1 --keyring-backend test. If no error occured, it is fixed well.

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[zsystm]

LGTM