fix(SelectMenu): multiple count error on page load

[NasrALdaya]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[benjamincanac]

I don't think this fix is correct, my guess is the selected computed introduced in #1349 is not taking the by key into account.

[cernymatej]

@benjamincanac While this does fix the problem in the linked issue, it doesn't resolve the underlying problem, which is that the selected computed property doesn't take the by prop into account.
I would approach it like this: #2228

[NasrALdaya]

@benjamincanac When the page loads and there are selected values, the selected computed property doesn't correctly reflect those values, leading to an incorrect length.
However, I noticed that props.modelValue.length always returns the correct length of the selected items.

[NasrALdaya]

@benjamincanac The filter condition isn't working on page load, and the selected computed property is empty.

The result:

const options = [
  { key: 'id', label: 'ID' },
  { key: 'title', label: 'Title' },
  { key: 'status', label: 'Status' }
]

const selected = ref([
  { key: 'id', label: 'ID' },
  { key: 'title', label: 'Title' }
])

[cernymatej]

@NasrALdaya I've already fixed it in my PR