Increase test coverage of PrivatekeyVault

[danielbate]

Per #753 to increase overall test coverage

Missing test coverage of a throw condition when getting a wallet

fuels-ts/packages/wallet-manager/src/vaults/privatekey-vault.ts

Lines 55 to 65 in 63c906b

	exportAccount(address: AbstractAddress): string {
	const privateKey = this.#privateKeys.find((pk) =>
	Wallet.fromPrivateKey(pk).address.equals(address)
	);
	if (!privateKey) {
	throw new Error('Address not found');
	}
	return privateKey;
	}