The bibliography uses the normal paragraph spacing value, which you can set for the whole document via
#set par(spacing: ...) // Default: 1.2em
Usually, the default value looks fine, but your increased line spacing makes it look disproportionate. If you want different spacing just for the bibliography, you can limit the above set rule or decrease the line spacing with a show-set rule
#show bibliography: set par(spacing: ..., leading: ...)
The default leading value (used for line spacing) is 0.65em.