ci: add support for loongarch64-unknown-linux-gnu

Author: heiher

.github/workflows/test.yml

@@ -135,6 +135,7 @@ jobs:
           - aarch64-unknown-linux-gnu
           - arm-unknown-linux-gnueabi
           - armv7-unknown-linux-gnueabihf
+          - loongarch64-unknown-linux-gnu
           - i686-unknown-linux-gnu
           - i686-unknown-linux-musl
           # No libstd available :(