itest: fix flake in address v2 test

[guggero]

We always expect two events. So asserting for just one only worked when things ran very quickly and only the first one was persisted. Always waiting for two will fix this timing-dependent flake.

Fixes the flake observed here: https://github.com/lightninglabs/taproot-assets/actions/runs/16798226160/job/47573276733?pr=1713

[coveralls]

Pull Request Test Coverage Report for Build 16824188448

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 71 unchanged lines in 14 files lost coverage.
• Overall coverage decreased (-0.05%) to 56.629%

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Files with Coverage Reduction	New Missed Lines	%
fn/context_guard.go	1	91.94%
asset/asset.go	2	80.23%
tapdb/mssmt.go	2	91.36%
tapdb/multiverse.go	2	81.4%
universe_rpc_diff.go	2	76.0%
universe/syncer.go	2	83.58%
itest/multisig.go	6	97.49%
tapdb/interfaces.go	6	82.5%
tapfreighter/chain_porter.go	6	81.75%
universe/archive.go	6	79.76%

Totals
Change from base Build 16818173014:	-0.05%
Covered Lines:	60543
Relevant Lines:	106912

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💛 - Coveralls

[jtobin]

LGTM