fix custom gas panel

[greg-schrammel]

Fixes APP-####

What changed (plus any additional context for devs)

fixes this https://github.com/rainbow-me/rainbow/pull/5885#pullrequestreview-2143148634

before / after (notice the estimated fee)

https://github.com/rainbow-me/rainbow/assets/6232729/72e1b0b9-615f-4fae-8da9-716b13108c5a

https://github.com/rainbow-me/rainbow/assets/6232729/0fe915db-3cb7-44bb-a488-73b51e2b343a

Screen recordings / screenshots

What to test

[jinchung]

try with:

• flashbots off
• update custom gas and miner tip to below 6 gwei (e.g, 5.6)
• turn flashbots on
• go back to custom gas - still shows previously set value of 5.6, until you hit the minus button and then it changes to 6 gwei and prevents the user from going below that again