Set useShareIndexes=true in availability_test.go

[rootulp]

Context

In celestia-app 0.7.0, there is a breaking change to the shares.Split.

This issue is a follow-up TODO from #1147

Problem

Unit tests in share/availability/light/availability_test.go currently set useShareIndexes=false because useShareIndexes=true will break unit tests unless we also update the transaction data used by tests to contain share indexes. This is non-trivial because the sample block used in the tests doesn't contain share indexes:

celestia-node/share/availability/light/availability_test.go

Lines 337 to 340 in 30ed57f

	// this is a sample block from devnet-2 which originally showed the issue with share ordering
	//
	//go:embed "testdata/block-825320.json"
	var sampleBlock string

Proposal

1. Update transaction data in test to contain share indexes
2. Set useShareIndexes=true
3. Remove TODO comment