[http_request] Fix usage of http response body (#17713)

Co-authored-by: J. Nick Koston <nick@koston.org>

esphome/components/http_request/http_request.h

@@ -488,10 +488,10 @@ template<typename... Ts> class HttpRequestSendAction final : public Action<Ts...
       body = this->body_.value(x...);
     }
     if (!this->json_.empty()) {
-      body = json::build_json([this, x...](JsonObject root) { this->encode_json_(x..., root); });
+      body = json::build_json([this, x...](JsonObject root) mutable { this->encode_json_(x..., root); });
     }
     if (this->json_func_ != nullptr) {
-      body = json::build_json([this, x...](JsonObject root) { this->json_func_(x..., root); });
+      body = json::build_json([this, x...](JsonObject root) mutable { this->json_func_(x..., root); });
     }
     std::vector<Header> request_headers;
     request_headers.reserve(this->request_headers_.size());

tests/components/http_request/http_request.yaml

@@ -59,6 +59,24 @@ esphome:
                   id: test_regression_light
                   brightness: 100%
                   effect: "None"
+      - http_request.get:
+          url: https://esphome.io
+          capture_response: true
+          on_response:
+            then:
+              # Regression test: http_request.post with json: (dict variant) inside
+              # on_response of a capture_response: true request puts std::string&
+              # (body) into the nested action's Ts..., which exposes a
+              # const-correctness bug in HttpRequestSendAction::play() where
+              # encode_json_ receives const copies of non-const reference args.
+              - http_request.post:
+                  url: https://esphome.io
+                  json:
+                    status: "ok"
+              # Same with json: lambda variant, exercises json_func_ path
+              - http_request.post:
+                  url: https://esphome.io
+                  json: !lambda "root[\"status\"] = \"ok\";"
 
 http_request:
   useragent: esphome/tagreader