fix: allow string slots

Author: iOvergaard

storyhelpers/render-slots.ts

@@ -34,7 +34,9 @@ function renderSlots(param: TemplateResult[] | Args) {
   // Join slots with consistent formatting; no extra line breaks between them
   const spacing = '  ';
 
-  const stringSlots = validSlots.map(slot => slot.strings[0]);
+  const stringSlots = validSlots.map(slot =>
+    typeof slot === 'string' ? slot : slot.strings?.[0] ?? '',
+  );
   const stringSlotsJoined = stringSlots.join('\n');
   const stringSlotsJoinedWithSpacing = stringSlotsJoined
     .split('\n')