chore: bump to next@15.4.0-canary.81 #5856

Job	Run time
Find path changes	16s
Rust lints	5m 58s
Turborepo rust check	5m 2s
Turborepo Integration (ubuntu-latest)	8m 32s
Turborepo Integration (windows-latest)	22m 56s
Turborepo Integration (macos-13)	21m 57s
Turborepo Rust testing on macos	8m 59s
Turborepo Rust testing on ubuntu	5m 59s
Turborepo Rust testing on windows	13m 16s
`with-tailwind` example	0s
`kitchen-sink` example	0s
`basic` example	0s
`with-svelte` example	0s
`non-monorepo` example	0s
Turborepo Test Summary	2s
Cleanup / cleanup	5s
	1h 33m 2s

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