Fix React 19 compat

[JoviDeCroock]

Resolves #622

Currently we import ReactCurrentDispatcher in the auto flow which won't work, however we already have an explicit error in the runtime that React 19 won't work. In a future major we can axe the auto runtime completely.

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🦋 Changeset detected

Latest commit: f338044

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@preact/signals-react-transform	Minor
@preact/signals-react	Minor

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[github-actions]

Size Change: +43 B (+0.05%)

Total Size: 83.3 kB

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docs/dist/assets/client.********.js	46.4 kB	+42 B (+0.09%)
docs/dist/nesting-********.js	1.13 kB	+1 B (+0.09%)

ℹ️ View Unchanged

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packages/core/dist/signals-core.js	1.45 kB
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packages/react-transform/dist/signals-transform.mjs	4.27 kB
packages/react-transform/dist/signals-transform.umd.js	5.15 kB
packages/react/dist/signals.js	188 B
packages/react/dist/signals.mjs	150 B

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