[CI] Test on mips targets (#271)

Author: joshlf

.github/workflows/ci.yml

@@ -40,6 +40,8 @@ jobs:
           "powerpc-unknown-linux-gnu",
           "powerpc64-unknown-linux-gnu",
           "riscv64gc-unknown-linux-gnu",
+          "mips-unknown-linux-gnu",
+          "mips64-unknown-linux-gnuabi64",
           "s390x-unknown-linux-gnu",
           "wasm32-wasi"
         ]