fix Path.Join (#644)

fixes #643

Author: CaringDev

src/System.IO.Abstractions/PathWrapper.cs

@@ -133,19 +133,19 @@ public override string GetRelativePath(string relativeTo, string path)
 #if FEATURE_PATH_JOIN_WITH_SPAN
         /// <inheritdoc />
         public override string Join(ReadOnlySpan<char> path1, ReadOnlySpan<char> path2) =>
-            Path.Join(path2, path2);
+            Path.Join(path1, path2);
 
         /// <inheritdoc />
         public override string Join(ReadOnlySpan<char> path1, ReadOnlySpan<char> path2, ReadOnlySpan<char> path3) =>
-            Path.Join(path2, path2, path3);
+            Path.Join(path1, path2, path3);
 
         /// <inheritdoc />
         public override bool TryJoin(ReadOnlySpan<char> path1, ReadOnlySpan<char> path2, Span<char> destination, out int charsWritten) =>
-            Path.TryJoin(path2, path2, destination, out charsWritten);
+            Path.TryJoin(path1, path2, destination, out charsWritten);
 
         /// <inheritdoc />
         public override bool TryJoin(ReadOnlySpan<char> path1, ReadOnlySpan<char> path2, ReadOnlySpan<char> path3, Span<char> destination, out int charsWritten) =>
-            Path.TryJoin(path2, path2, path3, destination, out charsWritten);
+            Path.TryJoin(path1, path2, path3, destination, out charsWritten);
 #endif
 
         public override bool IsPathRooted(string path)