truncate exceptions in GitHub summary tables to message + first stack frame (#5108)

GitHub summaries have limited data capacity. Previously, full exception
ToString() (type, message, and entire stack trace) was written to the
summary table. Now only the message and first line of the stack trace
are included, keeping summaries concise while still useful.

Author: thomhurst

TUnit.Engine/Reporters/GitHubReporter.cs

@@ -321,9 +321,9 @@ or TimeoutTestNodeStateProperty
         return stateProperty switch
         {
             FailedTestNodeStateProperty failedTestNodeStateProperty =>
-                failedTestNodeStateProperty.Exception?.ToString() ?? "Test failed",
+                GetTruncatedExceptionMessage(failedTestNodeStateProperty.Exception) ?? "Test failed",
             ErrorTestNodeStateProperty errorTestNodeStateProperty =>
-                errorTestNodeStateProperty.Exception?.ToString() ?? "Test failed",
+                GetTruncatedExceptionMessage(errorTestNodeStateProperty.Exception) ?? "Test failed",
             TimeoutTestNodeStateProperty timeoutTestNodeStateProperty => timeoutTestNodeStateProperty.Explanation,
 #pragma warning disable CS0618 // CancelledTestNodeStateProperty is obsolete
             CancelledTestNodeStateProperty => "Test was cancelled",
@@ -332,6 +332,25 @@ or TimeoutTestNodeStateProperty
         };
     }
 
+    private static string? GetTruncatedExceptionMessage(Exception? exception)
+    {
+        if (exception is null)
+        {
+            return null;
+        }
+
+        var message = exception.Message;
+
+        var firstStackTraceLine = exception.StackTrace?.Split('\n').FirstOrDefault()?.Trim();
+
+        if (string.IsNullOrWhiteSpace(firstStackTraceLine))
+        {
+            return message;
+        }
+
+        return $"{message}\n{firstStackTraceLine}";
+    }
+
     private static string GetStatus(IProperty? stateProperty)
     {
         return stateProperty switch