Fix use of invalidFmtError

src/path.zig

@@ -256,7 +256,7 @@ pub fn format(
     else if (@hasDecl(FormatOptions, fmt) and @TypeOf(@field(FormatOptions, fmt)) == FormatOptions)
         @field(FormatOptions, fmt)
     else
-        std.fmt.invalidFmtError(fmt, Path);
+        std.fmt.invalidFmtError(fmt, self);
 
     try self.write(opt, writer);
 }