`pattern` should only be applicable to the string type, and no other types

[Relequestual]

There's a Stackoverflow question that asks how you can validate the number of digits in a number using JSON Schema: https://stackoverflow.com/questions/53449740/how-can-i-validate-number-of-digits-in-a-number-using-json-schema-ajv/53449981

I explained, you cannot currently do this. Someone suggested you could use pattern, however it is only applicable to strings and not other types.

We have a test for checking pattern isn't applied to a bool, but no test to check that it isn't applied to a number.

There should be a test for checking that pattern isn't incorrectly applied to all other types. Some languages will stringify numbers.

[Julian]

This depends on #244.