Fix a bug where incorrect source locations were output for failing substructure tests

Author: ahoppen

Sources/_SwiftSyntaxTestSupport/SyntaxComparison.swift

@@ -76,14 +76,17 @@ extension TreeDifference: CustomDebugStringConvertible {
                 """
     }
 
+    let baselineRootConverter = SourceLocationConverter(file: "Baseline.swift", source: baseline.root.description)
+    let nodeRootConverter = SourceLocationConverter(file: "Actual.swift", source: node.root.description)
+
     return """
            \(message)
 
            Full Expected Tree:
-           \(baseline.root.debugDescription(includeChildren: true, includeTrivia: includeTrivia, converter: expectedConverter, mark: baseline))
+           \(baseline.root.debugDescription(includeChildren: true, includeTrivia: includeTrivia, converter: baselineRootConverter, mark: baseline))
 
            Full Actual Tree:
-           \(node.root.debugDescription(includeChildren: true, includeTrivia: includeTrivia, converter: actualConverter, mark: node))
+           \(node.root.debugDescription(includeChildren: true, includeTrivia: includeTrivia, converter: nodeRootConverter, mark: node))
            """
   }
 }