Revert "fix: concatenate all records into a single newline-separated …

…string for plaintext"

This reverts commit 1ad99dc.

target_s3/formats/format_plaintext.py

@@ -15,7 +15,7 @@ def _prepare_records(self):
         return super()._prepare_records()
 
     def _write(self) -> None:
-        return super()._write("\n".join(self.records))
+        return super()._write(self.records)
 
     def run(self) -> None:
         # use default behavior, no additional run steps needed