Incorrect kind is set for the argument token in the JSON output

RetDec emits incorrect kind for argument token in the JSON output.

Expected output:
```json
{
"kind": "i_fnc",
"val": "entry0"
},
{
"kind": "punc",
"val": "("
},
{
"kind": "type",
"val": "int64_t"
},
{
"kind": "ws",
"val": " "
},
{
"kind": **"i_arg",**
"val": "a1"
}
```

Output of RetDec:
```json
},
{
"kind": "i_fnc",
"val": "entry0"
},
{
"kind": "punc",
"val": "("
},
{
"kind": "type",
"val": "int64_t"
},
{
"kind": "ws",
"val": " "
},
{
"kind": **"i_lvar",**
"val": "a1"
}
```

https://github.com/avast/retdec/wiki/Decompiler-outputs

Start with the RetDec decompiler output documentation linked in the issue and trace how JSON tokens are classified for function arguments. Compare the reported output with the expected example, then verify that the argument token is emitted as "i_arg" rather than "i_lvar".

Written by the indexing model from the issue text.