Many are outdated for 1.20+, but texture-only packs often still work.
Installing a black villager texture pack is a straightforward process: black villager texture pack
This is the gold standard. While not exclusively a "black villager texture pack," Diverse Villagers is the most popular mod/texture hybrid that adds multiple skin tones, including deep brown and ebony hues. Many are outdated for 1
Several creators offer different takes on this concept, depending on whether you want a stylistic change or more diversity: Many are outdated for 1.20+