TS: isSpecifiedScalarType incorrectly refines type

[IvanGoncharov]

Reported by @yaacovCR in #2104 (comment)

This line -- I think -- causes typescript to assume that a type that fails isSpecifiedScalarType test is actually not a GraphqlScalarType at all.

graphql-js/tstypes/type/scalars.d.ts

Line 11 in a482d3b

export function isSpecifiedScalarType(type: any): type is GraphQLScalarType;

[IvanGoncharov]

Fixed in 14.5.8 📦
Long term solutions are proposed in #2194 and #2196