Update CODEOWNERS (dotnet#6105)

Add assignments for @dotnet/dotnet-extensions-ai-templates

Author: RussKie

.github/CODEOWNERS

@@ -25,6 +25,9 @@
 /src/Libraries/Microsoft.Extensions.AI.Evaluation.*                         @dotnet/dotnet-extensions-ai-evaluation
 /test/Libraries/Microsoft.Extensions.AI.Evaluation.*                        @dotnet/dotnet-extensions-ai-evaluation
 
+/src/ProjectTemplates                                                       @dotnet/dotnet-extensions-ai-templates
+/test/ProjectTemplates                                                      @dotnet/dotnet-extensions-ai-templates
+
 /src/Libraries/Microsoft.Extensions.Caching.Hybrid                          @dotnet/dotnet-extensions-caching-hybrid
 /src/Libraries/Microsoft.Extensions.Caching.Hybrid.*                        @dotnet/dotnet-extensions-caching-hybrid
 /test/Libraries/Microsoft.Extensions.Caching.Hybrid                         @dotnet/dotnet-extensions-caching-hybrid