Unformatted trace logging for step telemetry in ExecutionContext

Don't apply JSON formatting during the trace logging for step telemetry.
By default `StringUtil.ConvertToJson` uses `Formatting.Indented` which
causes multi-line logs for this particular json object.

The data contained in this particular log line is useful for operators
of self-hosted runners who are looking to use log aggregates to
understand their overall usage and performance. Parsing multi-line data
in log aggregates is very hard to get right, if not outright impossible
depending on how logs are aggregated.

src/Runner.Worker/ExecutionContext.cs

@@ -1145,7 +1145,7 @@ public void PublishStepTelemetry()
                         }
                     }
 
-                    Trace.Info($"Publish step telemetry for current step {StringUtil.ConvertToJson(StepTelemetry)}.");
+                    Trace.Info($"Publish step telemetry for current step {StringUtil.ConvertToJson(StepTelemetry, Formatting.None)}.");
                     Global.StepsTelemetry.Add(StepTelemetry);
                     _stepTelemetryPublished = true;
                 }