Confirm modal: Change 'fees' to 'costs' in the Receive label when no fees

[elena-zh]

Discussed in https://cowservices.slack.com/archives/C0361CDG8GP/p1725212579182209

To reproduce:

1. Open Swap form on any chain but Gnosis
2. Connect to a wallet
3. Specify a sell order
4. Press on the Swap button
5. Verify the 'Receive (before fees)' field at the top

AR: it says 'Receive (before fees)' when there is no fee

ER:

• when no fee, change the label to 'Receive (before costs)'
• when there is a fee (partner fee, volume fee o GC): leave the label as it is.