[python-nextgen] Fix binary response (#15076)

* fix binary response in python nextgen client

* update samples

samples/client/echo_api/java/feign-gson/api/openapi.yaml

@@ -326,6 +326,22 @@ paths:
       - body
       x-content-type: application/json
       x-accepts: text/plain
+  /binary/gif:
+    post:
+      description: Test binary (gif) response body
+      operationId: test/binary/gif
+      responses:
+        "200":
+          content:
+            image/gif:
+              schema:
+                format: binary
+                type: string
+          description: Successful operation
+      summary: Test binary (gif) response body
+      tags:
+      - body
+      x-accepts: image/gif
 components:
   requestBodies:
     Pet:

samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/api/BodyApi.java

@@ -4,6 +4,7 @@ import org.openapitools.client.ApiClient;
 import org.openapitools.client.EncodingUtils;
 import org.openapitools.client.model.ApiResponse;
 
+import java.io.File;
 import org.openapitools.client.model.Pet;
 
 import java.util.ArrayList;
@@ -16,6 +17,31 @@ import feign.*;
 public interface BodyApi extends ApiClient.Api {
 
 
+  /**
+   * Test binary (gif) response body
+   * Test binary (gif) response body
+   * @return File
+   */
+  @RequestLine("POST /binary/gif")
+  @Headers({
+    "Accept: image/gif",
+  })
+  File testBinaryGif();
+
+  /**
+   * Test binary (gif) response body
+   * Similar to <code>testBinaryGif</code> but it also returns the http response headers .
+   * Test binary (gif) response body
+   * @return A ApiResponse that wraps the response boyd and the http headers.
+   */
+  @RequestLine("POST /binary/gif")
+  @Headers({
+    "Accept: image/gif",
+  })
+  ApiResponse<File> testBinaryGifWithHttpInfo();
+
+
+
   /**
    * Test body parameter(s)
    * Test body parameter(s)