Fix telemetry sample bug (#5037)

Author: westey-m

dotnet/samples/02-agents/AgentOpenTelemetry/Program.cs

@@ -23,7 +23,7 @@
 const string ServiceName = "AgentOpenTelemetry";
 
 // Configure OpenTelemetry for Aspire dashboard
-var otlpEndpoint = Environment.GetEnvironmentVariable("OTEL_EXPORTER_OTLP_ENDPOINT") ?? "http://localhost:4318";
+var otlpEndpoint = Environment.GetEnvironmentVariable("OTEL_EXPORTER_OTLP_ENDPOINT") ?? "http://localhost:4317";
 
 var applicationInsightsConnectionString = Environment.GetEnvironmentVariable("APPLICATIONINSIGHTS_CONNECTION_STRING");