Default coords do not replace user coords

[teunbrand]

This PR aims to fix #6572.

It does what is says in the title. Reprex from the linked issue:

devtools::load_all("~/packages/ggplot2/")

world <- rnaturalearth::ne_countries()

ggplot(world) +
  coord_sf(crs = "+proj=moll") +
  geom_sf()

^{Created on 2025-08-22 with reprex v2.1.1}