docs(mocktail): use same pattern for stubbing

[davidlj95]

Status

READY

Breaking Changes

NO

Description

Noticed that in last section of README.md , about the Why am I seeing error: type 'Null' is not a subtype of type 'Future<void>'? issue, the example stubs without adding a callback. Propose to use a callback there to avoid misunderstandings. Despite anyway it's equivalent, if the guide consistently reminds using callbacks, I think would be nice to use them in that example too.

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [x] 📝 Documentation
• [ ] 🗑️ Chore