chore: Release library Google.Cloud.Dialogflow.V2 version 4.28.0

### New features

- Updated v2 dialogflow client libraries

### Documentation improvements

- Updated v2 dialogflow client libraries

Librarian-Release-Library: Google.Cloud.Dialogflow.V2
Librarian-Release-Version: 4.28.0
Librarian-Release-ID: release-20251215T140123Z

Author: google-cloud-sdk-librarian-dotnet-robot

apis/Google.Cloud.Dialogflow.V2/Google.Cloud.Dialogflow.V2/Google.Cloud.Dialogflow.V2.csproj

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Version>4.27.0</Version>
+    <Version>4.28.0</Version>
     <TargetFrameworks>netstandard2.0;net462</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <Description>Recommended Google client library to access the Google Dialogflow API (v2).</Description>

apis/Google.Cloud.Dialogflow.V2/docs/history.md

@@ -1,5 +1,15 @@
 # Version history
 
+## Version 4.28.0, released 2025-12-15
+
+### New features
+
+- Updated v2 dialogflow client libraries
+
+### Documentation improvements
+
+- Updated v2 dialogflow client libraries
+
 ## Version 4.27.0, released 2025-11-05
 
 ### New features

generator-input/apis.json

@@ -2380,7 +2380,7 @@
       "protoPath": "google/cloud/dialogflow/v2",
       "productName": "Google Cloud Dialogflow",
       "productUrl": "https://cloud.google.com/dialogflow-enterprise/",
-      "version": "4.27.0",
+      "version": "4.28.0",
       "type": "grpc",
       "description": "Recommended Google client library to access the Google Dialogflow API (v2).",
       "tags": [

generator-input/pipeline-state.json

@@ -1398,12 +1398,12 @@
         },
         {
             "id": "Google.Cloud.Dialogflow.V2",
-            "currentVersion": "4.27.0",
+            "currentVersion": "4.28.0",
             "generationAutomationLevel": "AUTOMATION_LEVEL_AUTOMATIC",
             "releaseAutomationLevel": "AUTOMATION_LEVEL_AUTOMATIC",
-            "releaseTimestamp": "2025-11-05T16:44:31.326651985Z",
+            "releaseTimestamp": "2025-12-15T14:05:27.599309526Z",
             "lastGeneratedCommit": "7a595fde9d62010213670dee0fdf4753e047b020",
-            "lastReleasedCommit": "888ae95dd6125f754650d55410b8c117b618a268",
+            "lastReleasedCommit": "7a595fde9d62010213670dee0fdf4753e047b020",
             "apiPaths": [
                 "google/cloud/dialogflow/v2"
             ],