Fix for position_stack(vjust)

[teunbrand]

This PR aims to fix #6692.

The problem was #5789 skipping too eagerly.

Reprex from issue:

devtools::load_all("~/packages/ggplot2/")
#> ℹ Loading ggplot2

test <- tibble::tibble(bin = seq(3), count = c(23,22,10))

ggplot(test, aes(x = bin, y = count))+
  geom_col()+
  geom_text(
    aes(label = round(count, 2)),
    position = position_stack(vjust = 0.5)
  )

^{Created on 2025-10-10 with reprex v2.1.1}

[thomasp85]

LGTM