NuGet: Bump Microsoft.Agents.AI.A2A from 1.0.0-preview.251125.1 to 1.0.0-preview.251204.1

---
updated-dependencies:
- dependency-name: Microsoft.Agents.AI.A2A
  dependency-version: 1.0.0-preview.251204.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Versions.props

@@ -10,7 +10,7 @@
     <MsExtVersion>10.0.0</MsExtVersion>
     <MsTestVersion>2.0.2</MsTestVersion>
     <ToolKitVersion>13.0.0</ToolKitVersion>
-    <AgentFrameworkVersion>1.0.0-preview.251125.1</AgentFrameworkVersion>
+    <AgentFrameworkVersion>1.0.0-preview.251204.1</AgentFrameworkVersion>
     <!-- Observability & Health -->
     <HealthChecksVersion>9.0.0</HealthChecksVersion>
   </PropertyGroup>