Disambiguate "aggregate rows" in the xml_schema changelog entry

In DMARC vocabulary "row" reads as the <row> element inside an
aggregate report record, which carries no schema information — the
changelog entry was about the flattened JSON/CSV output lines, where
xml_schema is a synthesized per-record field. Reword the entry and the
two related comments to say which kind of row is meant.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

google_secops_parser/parsedmarc.conf

@@ -244,8 +244,9 @@ filter {
   #    xml_schema is aggregate-only and guaranteed non-empty: the <feedback>
   #    XML root element is what identifies an aggregate report, and parsedmarc
   #    falls back to "draft" whenever <version> is missing, empty, or
-  #    whitespace (parsedmarc/__init__.py), so every aggregate row carries a
-  #    usable value. It is preferred over: header_from (can be empty when a
+  #    whitespace (parsedmarc/__init__.py), so every JSON line serialized
+  #    from an aggregate report carries a usable value. It is preferred
+  #    over: header_from (can be empty when a
   #    record carries no identifiers), adkim (a defaulted policy field), domain
   #    (a generic name), and dmarc_aligned (a boolean that only becomes testable
   #    after the convert in step 1b -- detection should not depend on that).