.dir-locals.el: Add geiser-insert-actual-lambda.
Guix project seems to prefer using lambda over λ. Express that preference for Geiser users by setting the geiser-insert-actual-lambda variable to nil. In the 0.31 version it will affect how geiser-insert-lambda works, making it insert lambda string (instead of the current λ.
- .dir-locals.el (nil): Add geiser-insert-actual-lambda set to nil.