You are actually not breaking Liskov's Substitution Principle. Liskov's says
objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program
In your case you can. With your interpretation of Liskov almost no inheritance and extensions of classes will be allowed.
I think that a ICustomerRepository that "inherents" from IRepository would be just fine. I can still replace ICustomerRepository everywhere where I would use IRepostory (given ICustomerRepository:IRepostory)
Liskov guards against unexpected behavior of subclasses. The most used (although not necessarily the beste) example seems to be the example where a square inherets from a rectangle. Here we have a SetWidth method that is overridden by Square, but Square also sets the height since it is a square. The original methods definition is therefore changed in the subclass and therefore violates the principle.