Test on loongarch

Author: andrjohns

.github/workflows/R-CMD-check-cross.yaml

@@ -21,6 +21,7 @@ jobs:
           -  { platform: ppc64le }
           -  { platform: s390x }
           -  { platform: riscv64 }
+          -  { platform: loong64 }
           -  { platform: FreeBSD }
 
     env: