Fix typo in source migration docs (dest -> test) (#5956)

Author: jamesonwilliams

docs/source/migration/4.0.mdx

@@ -465,7 +465,7 @@ The [Android Studio plugin](../testing/android-studio-plugin#migration-helpers)
 
 Test builders were an experimental feature that have been superseded by [data builders](../testing/data-builders), a simpler version that also plays nicer with custom scalars.
 
-In Apollo Kotlin 4.0, dest builders are no longer available - please refer to the data builders documentation for more information.
+In Apollo Kotlin 4.0, test builders are no longer available - please refer to the data builders documentation for more information.
 
 ### Enum class names now have their first letter capitalized