Disambiguate fakeit::Prototype<...>::MemberType parsing

[seva-deriv]

Add template keyword as required by C++ standard

[coveralls]

Coverage remained the same at 99.925% when pulling 5a48e74 on seva-deriv:master into 96f193e on eranpeer:dev-2.3.1.

[FranckRJ]

Thanks for the fix. Just out of curiosity, did you had any issue before adding that keyword, and if so with which compiler / what kind of code ?

And also, usually we don't change what's inside the single_header directory, it's only generated once before a release. If you can revert these changes it would be better but it's not a big deal anyway I can do it myself.

[seva-deriv]

OK, I'll revert.
I faced the compilation error on clang/clang-cl 14.0.1. But the use case was not straightforward. It was in "disabled" context in expression like if constexpr (eval_to_false) { <HERE> }.