Add `riscv64gc-unknown-linux-gnu` into target list in build-manifest
Add `riscv64gc-unknown-linux-gnu` into target list in build-manifest

Missed in #68037 

r? @alexcrichton
graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust