tests, signer: remove staticcheck warnings (#20364)

signer/core/api.go

signer/core/api_test.go

signer/core/cliui.go

signer/core/stdioui.go

signer/core/types.go

signer/core/uiapi.go

signer/rules/deps/bindata.go

signer/rules/rules.go

signer/storage/storage.go

tests/block_test_util.go

tests/init_test.go

tests/transaction_test_util.go