Use bytes rather than native string for result (#46281)

This prevents a stack trace in Python 3 when the result is an empty file since
the file is open in binary mode and a native string in Python 3 is str,
not bytes.

lib/ansible/modules/files/blockinfile.py

@@ -309,7 +309,7 @@ def main():
         if original is None or original.endswith(b('\n')):
             result += b('\n')
     else:
-        result = ''
+        result = b''
 
     if module._diff:
         diff['after'] = result