Fix partial matching in geom_violin()

[teunbrand]

This PR aims to fix #5374.

Briefly, it solves a partial matching bug that would accept weights as the weight aesthetic.
Specifying weights now just throws a warning, instead of being accidentally used as the weight aesthetic.

devtools::load_all("~/packages/ggplot2/")
#> ℹ Loading ggplot2
options(warnPartialMatchDollar = TRUE)

p <- ggplot(iris, aes(Species, Sepal.Width)) + 
  geom_violin(aes(weights = Sepal.Length))
#> Warning in geom_violin(aes(weights = Sepal.Length)): Ignoring unknown
#> aesthetics: weights

^{Created on 2023-08-02 with reprex v2.0.2}

[thomasp85]

LGTM