Use correct stash name when running nightly tests (apache#14809)

The PR apache#14570 has
introduced a bug where the "stash name" is not matching:

- It is **packed** as `ubuntu_cpu_int64`
- It is **unpacked** as `cpu_int64`

tests/nightly/JenkinsfileForBinaries

@@ -46,7 +46,7 @@ core_logic: {
         ws('workspace/build-cpu-int64') {
           utils.init_git()
           utils.docker_run('ubuntu_nightly_cpu', 'build_ubuntu_cpu_large_tensor', false)
-          utils.pack_lib('ubuntu_cpu_int64', mx_cmake_lib, true)
+          utils.pack_lib('cpu_int64', mx_cmake_lib, true)
         }
       }
     },
@@ -55,7 +55,7 @@ core_logic: {
         ws('workspace/build-gpu-int64') {
           utils.init_git()
           utils.docker_run('ubuntu_nightly_gpu', 'build_ubuntu_gpu_large_tensor', true)
-          utils.pack_lib('ubuntu_gpu_int64', mx_cmake_lib, true)
+          utils.pack_lib('gpu_int64', mx_cmake_lib, true)
         }
       }
     }