fix(index.d.ts): allow 2 generic types in mongoose.model function

[synsh]

fixes #9678

[icopp]

From my testing with something similar on an existing codebase, it looks like there may still be some issues here with methods like create, which will expect that the methods from the statics are included on the supplied object. Fixing it may take changing the Model definition to directly accommodate statics as a generic type param which create and the like can then exclude.

[vkarpov15]

Thanks 👍