docs: migration guide

Author: AriPerkkio

docs/guide/migration.md

@@ -123,6 +123,7 @@ Vitest 4.0 removes some deprecated APIs, including:
 - `poolMatchGlobs` config option. Use [`projects`](/guide/projects) instead.
 - `environmentMatchGlobs` config option. Use [`projects`](/guide/projects) instead.
 - `workspace` config option. Use [`projects`](/guide/projects) instead.
+- Reporter APIs `onCollected`, `onSpecsCollected`, `onPathsCollected`, `onTaskUpdate` and `onFinished`. See [`Reporters API`](/advanced/api/reporters) for new alternatives. These APIs were introduced in Vitest `v3.0.0`.
 
 This release also removes all deprecated types. This finally fixes an issue where Vitest accidentally pulled in `node` types (see [#5481](https://github.com/vitest-dev/vitest/issues/5481) and [#6141](https://github.com/vitest-dev/vitest/issues/6141)).