blob copy failed when requires sync

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**Describe the bug**
az storage blob copy start with --requires-sync failed on block blob with CannotVerifyCopySource error.
the copy is successful if remove the --requires-sync

**To Reproduce**
az storage blob copy start ....... --requires-sync

**Expected behavior**
The copy operatiion returns on completion without any error.

**Environment summary**

Install Method: interactive script

CLI version:
azure-cli 2.16.0
core 2.16.0
telemetry 1.0.6
Python location '/usr/bin/python3'
Extensions directory '/home/jiancheng/.azure/cliextensions'
Python (Linux) 3.6.8 (default, Nov 16 2020, 16:55:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)]
Your CLI is up-to-date.

OS version: CentOS 7
Shell Type: bash

**Additional context**