Add minor missing points to Preimage test

[rockbmb]

#453 (and its PR #471) have left the preimages pallet with good end-to-end test coverage.

Two outstanding points remain:

1. the test to ensureUpdated needs a fix regarding the check of transaction fee waiving
   

   polkadot-ecosystem-tests/packages/shared/src/preimage.ts

   Lines 730 to 744 in 20f9bf5

   	/**
   	* Test the "ensure_updated" preimage functionality.
   	*
   	* 1. Simulate a number of pre-deprecation preimages with bogus hashes.
   	* 2. Alice registers a number of post-deprecation (valid) preimages.
   	* 3. Ensure that all valid preimages have been registered.
   	* 4. Alice calls "ensure_updated" for all hashes (valid and bogus).
   	* 5. Verify that Alice's reserved funds remain the same after the update.
   	* 6. If the ratio of new to total preimages is less than 90%, check that fees have been paid.
   	*/
   	async function preimageEnsureUpdatedTest<
   	TCustom extends Record<string, unknown> | undefined,
   	TInitStorages extends Record<string, Record<string, any>> | undefined,
   	>(chain: Chain<TCustom, TInitStorages>, oldPreimagesCount: number, newPreimagesCount: number) {
   	const [client] = await setupNetworks(chain)

2. the test to excessively large preimages is currently not submitting the preimage it generates
   

   polkadot-ecosystem-tests/packages/shared/src/preimage.ts

   Lines 695 to 712 in 20f9bf5

   	/**
   	* Test the registering (noting) and unregistering (unnoting) of an oversized preimage.
   	*
   	* 1. Alice registers an oversized preimage.
   	* 2. The registration fails and no preimage is stored.
   	*/
   	async function preimageOversizedTest<
   	TCustom extends Record<string, unknown> | undefined,
   	TInitStorages extends Record<string, Record<string, any>> | undefined,
   	>(chain: Chain<TCustom, TInitStorages>) {
   	const [client] = await setupNetworks(chain)
   	const alice = testAccounts.alice
   	setupBalances(client, [{ address: alice.address, amount: 1000e10 }])
   	// 1. Alice registers an oversized preimage (more than 4 MB).
   	const maxPreimageSize = 4 * 1024 * 1024
   	const oversizedBytes = new Uint8Array(maxPreimageSize + 1).fill(1)

This PR is to address these minor issues.