fix: search changelogs down to fourth heading deep

Closes #1687

lib/workers/pr/release-notes.js

@@ -93,8 +93,23 @@ async function getReleaseNotesMd(repository, version) {
     logger.trace('Could not parse top level headings. Trying second level');
     changelogParsed = changelogMd.match(/^##([^#]+?)\n([^]+?)(?=^##[^#])/gm);
     if (!changelogParsed || changelogParsed.length === 1) {
-      logger.info({ repository }, 'No second level changelogs headings found');
-      return null;
+      logger.debug({ repository }, 'No second level changelogs headings found');
+      changelogParsed = changelogMd.match(
+        /^###([^#]+?)\n([^]+?)(?=^###[^#])/gm
+      );
+      if (!changelogParsed || changelogParsed.length === 1) {
+        logger.debug(
+          { repository },
+          'No second third changelogs headings found'
+        );
+        changelogParsed = changelogMd.match(
+          /^####([^#]+?)\n([^]+?)(?=^####[^#])/gm
+        );
+        if (!changelogParsed || changelogParsed.length === 1) {
+          logger.info({ repository }, 'No changelogs headings found');
+          return null;
+        }
+      }
     }
   }
   for (const section of changelogParsed) {