Fix insert false positives in SkipsModelValidations

[eugeneius]

Adding insert to the forbidden methods list for SkipsModelValidations in #289 introduced false positives, particularly since String#insert and Array#insert are commonly used.

We can reduce the impact by matching on the arguments: Active Record's insert method takes one positional argument and two optional keyword arguments (:returning and :unique_by). Anything else can be ignored.

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[koic]

Thanks!