Add tutors with the same phone number

[nus-pe-bot]

It is possible to add tutors with the same handphone number, when it is impossible for such an occurrence to happen.

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_{[original: nus-cs2103-AY2223S1/pe-interim#464] [original labels: type.FeatureFlaw severity.Medium]}

[fannyjian]

Team's Response

This is very unlikely to happen since it is extremely unlikely that tutors will have the same phone numbers, so our current check for duplicate tutors is sufficient for most situations.

Duplicate status (if any):

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