refactor: remove unnecessary `Box` from into_inner #271

Job	Run time
cargo-publish	0s
Tests (macos-latest, stable)	1m 24s
Tests (macos-latest, beta)	1m 5s
Tests (macos-latest, nightly)	1m 11s
Tests (windows-latest, stable)	1m 12s
Tests (windows-latest, beta)	1m 1s
Tests (windows-latest, nightly)	1m 6s
Tests (ubuntu-latest, stable)	33s
Tests (ubuntu-latest, beta)	33s
Tests (ubuntu-latest, nightly)	35s
	8m 40s

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