Rename variable 'filename' to 'file_name'

This fixes #57

Author: flo1o1

src/meshcore_cli/meshcore_cli.py

@@ -3606,7 +3606,7 @@ async def next_cmd(mc, cmds, json_output=False):
             case "script" :
                 if len(cmds) > 1:
                     argnum = 1
-                    filename = cmds[1]
+                    file_name = cmds[1]
                 else:
                     file_name = await prompt_for_file()
                 if not file_name is None: