Fix double phone vote

[Stef-Rousset]

Problem:
If i create an account with no phone number, I can the vote and enter a phone number that already belongs to another account, and vote twice with the same phone number

Related Issues:
Notion card => https://www.notion.so/opensourcepolitics/bd4bf860eab94f9daca7da803f09e3b2?v=c96df65755dd403d95e86f82d7749709&p=39467ef809e94526bf88fee4516f89f3&pm=c

Testing:

1. As a user, create an account with email
2. As user, go to Assemblies > choose one assembly > go to budgets > choose one budget > vote by providing a phone number
3. As a second user, create an account with email
4. As a second user, go to Assemblies > choose one assembly > go to budgets > choose one budget > vote by providing the same phone number/phone country provided by first user
5. Notice that you have a message that indicates phone number is not available and you must provide another number

If you have time, you can also check that those paths still work well:

1. As a user not signed in, vote with only your phone number (anonymous user)
2. As a user not signed in, vote with only your phone number by providing the same phone number already linked to an account and note that you are signed in and not anonymous user anymore

Tasks:
Add specs

[BarbaraOliveira13]

I ran it, works 🎉

[Quentinchampenois]

Hello, just a change request

[Quentinchampenois]

Suggested change

	return broadcast(:invalid, "non disponible") if registered_user_with_same_phone_and_country?
	return broadcast(:invalid, :already_exist) if registered_user_with_same_phone_and_country?

Prefer to use symbol rather than french translation

[Quentinchampenois]

Suggested change

	flash.now[:alert] = if error_code == "non disponible"
	flash.now[:alert] = if error_code == :already_exist