Unit Tests crashes on hardware

After running unit tests, sometimes the app crashes with the following:
```
Terminating app due to uncaught exception 'RLMException', reason: 'Object has been deleted or invalidated.'
terminating with uncaught exception of type NSException
```
This appears to happen on hardware only (iPhone6SPlus/iOS14.8.1) and under the following condition:

**Testing**
1. Delete AlphaWallet
2. Run the AlphaWallet Unit Tests

**Expects**
3. All tests to conclude without crashing.

However, if I first run AlphaWallet twice, this crash does not happen.

When running under iPhoneX/iOS15.2, I experience the following in `testSignPersonalMessageWithRawPrivateKey()` on `let data = try! signResult.dematerialize()`.
```swift
AlphaWalletTests/EtherKeystoreTests.swift:160: Fatal error: 'try!' expression unexpectedly raised an error: AlphaWallet.KeystoreError.accountMayNeedImportingAgainOrEnablePasscode
```