add azure-core to azure-mgmt-storagesync dev_reqs (Azure#27806)

Author: scbedd

sdk/storage/azure-mgmt-storagesync/dev_requirements.txt

@@ -1,4 +1,5 @@
 -e ../../../tools/vcrpy
 -e ../../../tools/azure-sdk-tools
 -e ../../../tools/azure-devtools
--e ../../core/azure-mgmt-core
+-e ../../core/azure-mgmt-core
+-e ../../core/azure-core