Fix remote signer test (#2400)

## Proposed Changes

Unescape text for json comparison in:

3a24ca5f14/remote_signer/tests/sign.rs (L282-L285)

Which causes this error:

```
---- sign::invalid_field_fork stdout ----
thread 'sign::invalid_field_fork' panicked at 'assertion failed: `(left == right)`
  left: `"Unable to parse body message from JSON: Error(\"invalid hex (InvalidHexCharacter { c: 'I', index: 0 })\", line: 1, column: 237097)"`,
 right: `"Unable to parse body message from JSON: Error(\"invalid hex (InvalidHexCharacter { c: \\'I\\', index: 0 })\", line: 1, column: 237097)"`', testing/remote_signer_test/src/consumer.rs:144:5
```

This is my first contribution and happy to receive feedback if you have any. Thanks

testing/remote_signer_test/src/consumer.rs

@@ -141,5 +141,12 @@ pub fn assert_sign_ok(resp: ApiTestResponse, expected_signature: &str) {
 
 pub fn assert_sign_error(resp: ApiTestResponse, http_status: u16, error_msg: &str) {
     assert_eq!(resp.status, http_status);
-    assert_eq!(resp.json["error"].as_str().unwrap(), error_msg);
+    assert_eq!(
+        resp.json["error"]
+            .as_str()
+            .unwrap()
+            // cross-platform compatiblity
+            .replace("\\", ""),
+        error_msg
+    );
 }