Add trailing newline to markdown report

Without trailing newline in a markdown report, the first additional information that comes from cmdline handler will end up in an additional row below the TOTALs row.

E.g. Coverage failure: https://github.com/nedbat/coveragepy/blob/master/coverage/cmdline.py#L761

coverage/report.py

@@ -108,6 +108,8 @@ def _report_text(
         for end_line in end_lines:
             self.write(end_line)
 
+        self.write("")
+
     def _report_markdown(
         self,
         header: list[str],