fix: Use listOfFailedFiles as a global variable

Author: chrisburr

src/DIRAC/DataManagementSystem/scripts/dirac_dms_directory_sync.py

@@ -503,6 +503,8 @@ def run(parameters, delete, nthreads):
 
 @DIRACScript()
 def main():
+    global listOfFailedFiles
+
     Script.registerSwitch("D", "sync", "Make target directory identical to source")
     Script.registerSwitch("j:", "parallel=", "Multithreaded download and upload")
     Script.parseCommandLine(ignoreErrors=False)