fix: avoid regenerating mnemonics on back button hit

[NeOMakinG]

Description

If you go back from backup test, the mnemonic should be the same as previously selected

If you go back after successfuly passing the test, the mnemonic should be a new one as it's sealed

Issue (if applicable)

closes #8874

Risk

High Risk PRs Require 2 approvals

What protocols, transaction types, wallets or contract interactions might be affected by this PR?

Testing

• Try to create a new wallet
• Go back from one of the back up test
• Verify the mnemonic, it should be the same
• It should change only if you come from another page or from the wallet password/name screen as you already saved this mnemonic somewhere

Engineering

n/a

Operations

n/a

• 🏁 My feature is behind a flag and doesn't require operations testing (yet)

Screenshots (if applicable)

https://jam.dev/c/ea989cb5-7bb3-40d7-9e33-2cc9503ab391

[gomesalexandre]

Tested locally, LGTM! Some non-blocking comments to tackle at your convenience

https://jam.dev/c/f975e7d5-18a2-4fee-bb80-8ac5c22d0e5c