Add tests for options with G, GB and GiB suffixes

tests/cli-tests/basic/memlimit.sh.stdout.exact

@@ -11,3 +11,12 @@
 + zstd --memory=1M file
 + zstd --memory=1MB file
 + zstd --memory=1MiB file
++ zstd --memory=1G file
++ zstd --memory=1GB file
++ zstd --memory=1GiB file
++ zstd --memory=3G file
++ zstd --memory=3GB file
++ zstd --memory=3GiB file
++ zstd --memory=4G file
++ zstd --memory=4GB file
++ zstd --memory=4GiB file