String "vignettes" in path to static images get replaced by "articles"

The issue:

under vignettes/: an file a_file.Rmd, with a chunk that includes a static image
```
knitr::include_graphics("../man/figures/vignettes/a/b/c/image.png")
```
a static image file under man/figures/vignettes/a/b/c/image.png

When building the site, I get the warning:

Missing images in vignettes/a_file.Rmd:
../reference/figures/articles/a/b/c/image.png
ℹ pkgdown can only use images in man/figures and vignettes

The generated HTML source indeed refers to ../reference/figures/articles/a/b/c/image.png
But, the actual image has been copied under ../reference/figures/vignettes/a/b/c/image.png

The cause:

Hence, it looks like there is some string substitution happening, which replaces "vignettes" by "articles", which in this case is incorrect or at least not consistent with where the image files are copied to. I believe this happens here: https://github.com/r-lib/pkgdown/blob/ffe60d5f60934e95285d416dae12c05e24ed1dac/R/tweak-tags.R#L93

r-lib / pkgdown