No bug: Wallet unit test fixup

[StephenHeaps]

Summary of Changes

• Resolve AccountActivityStoreTests.testUpdateEthereumAccount() flakey test
• Disabled:
  • TransactionConfirmationStoreTests.testPrepareERC20Approve()
  • TransactionConfirmationStoreTests.testPrepareTransactionNotOnSelectedNetwork()
• Updated disabled SendTokenStoreTests tests. Reduced from 11 disabled tests to 6.
• Opened Resolve Flakey Wallet Tests #7757 to resolve the disabled tests.

This pull request fixes #

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()
• New or updated UI has been tested across:
  • Light & dark mode
  • Different size classes (iPhone, landscape, iPad)
  • Different dynamic type sizes

Test Plan:

1. In the Brave.xctestplan, disable each of the disabled tests in our Fastfile
2. In Xcode, open Test navigator panel
3. Right-click on BraveWalletTests and select Run "BraveWalletTests" Repeatedly...

4. Change Stop After to maximum repetitions and set Maximum Repetitions to >100 (100 wasn't catching them all, I used 1000 but less likely suffices).

5. Click Run
6. Make sure no other tests are failing.

Screenshots:

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue and pull request is assigned to a milestone (should happen at merge time).