rpc: fix the stop response

[vincenzopalazzo]

Find on lampo ci

stack backtrace:
0: rust_begin_unwind
1: core::panicking::panic_fmt
2: core::result::unwrap_failed
3: core::result::Result<T,E>::unwrap
at /build/rustc-1.75.0-src/library/core/src/result.rs:1077:23
4: tests::lampo_cln_tests::test_lampo_to_cln_close_channel_with_channel_id_success
at ./src/lampo_cln_tests.rs:985:5
5: tests::lampo_cln_tests::test_lampo_to_cln_close_channel_with_channel_id_success::{{closure}}
at ./src/lampo_cln_tests.rs:887:61
6: core::ops::function::FnOnce::call_once
at /build/rustc-1.75.0-src/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with RUST_BACKTRACE=full for a verbose backtrace.

---- lampo_cln_tests::test_lampo_to_cln_close_channel_without_channel_id_success stdout ----
thread 'lampo_cln_tests::test_lampo_to_cln_close_channel_without_channel_id_success' panicked at tests/tests/src/lampo_cln_tests.rs:1087:28:
called Result::unwrap() on an Err value: JSON decode error: invalid type: map, expected a string at line 1 column 36

vincenzopalazzo/lampo.rs#249