Update bytes str code (flutter/engine#39275)

engine/src/flutter/tools/fuchsia/merge_and_upload_debug_symbols.py

@@ -64,6 +64,7 @@ def CheckCIPDPackageExists(package_name, tag):
       tag,
   ]
   stdout = subprocess.check_output(command)
+  stdout = stdout if isinstance(stdout, str) else stdout.decode('UTF-8')
   match = re.search(r'No matching instances\.', stdout)
   if match:
     return False