fix(typescript): Make b64 header optional

[bespokebob]

The b64 header is currently defined as a required field, so omitting it throws a typescript error. Since its type is defined as "never", there is nothing that can be assigned to it, making it impossible to actually use.
This makes b64 optional, which still prevents assigning to it due to the type.

[bespokebob]

Error before fix, when b64 is omitted:

Argument of type '{ alg: string; }' is not assignable to parameter of type 'JWTHeaderParameters'.
  Property 'b64' is missing in type '{ alg: string; }' but required in type 'JWTHeaderParameters'.ts(2345)

(Correct) error trying to assign to b64 before fix:

Type 'boolean' is not assignable to type 'never'.ts(2322)
types.d.ts(265, 3): The expected type comes from property 'b64' which is declared here on type 'JWTHeaderParameters'

Attempting to assign to b64 after fix:

Type 'false' is not assignable to type 'undefined'.ts(2322)
types.d.ts(265, 3): The expected type comes from property 'b64' which is declared here on type 'JWTHeaderParameters'

Which is an odd error, but I guess TypeScript is treating b64?: never as never | undefined which would be the same as undefined? Actually defining that field as b64: undefined still gives the "required" error, though.

[panva]

@youngbob thank you for catching this, i'll release a fix with this as soon as CI passes.

[panva]

https://github.com/panva/jose/releases/tag/v4.3.5

[CMCDragonkai]

I had some code inherited that set the b64 to true. Now TSC is complaining that true is not assignable type undefined. How is this supposed to work?

[panva]

Ah yeah. Only false should be forbidden for JWTs... will fix. Nevertheless setting it to true is the same as omitting it.

[panva]

https://github.com/panva/jose/releases/tag/v4.3.7