Go ahead and re-combine the two feed includes

After discussion, having an absolute URL in the generated HTML is just
fine.

Author: jepler

_includes/downloads/board_image.html

@@ -1,7 +1,7 @@
-  {% assign small_image = "/assets/images/boards/small/" | append: include.board_image %}
-  {% assign large_image = "/assets/images/boards/large/" | append: include.board_image %}
-  <img srcset="{{ small_image }} 300w,
-               {{ large_image }} 700w"
-       sizes="(max-width: 1024px) 700px,
-              300px"
-       src="{{ large_image }}" alt="Image of Board" loading="lazy">
+{% assign small_image = "/assets/images/boards/small/" | append: include.board_image | absolute_url %}
+{% assign large_image = "/assets/images/boards/large/" | append: include.board_image | absolute_url %}
+<img srcset="{{ small_image }} 300w,
+             {{ large_image }} 700w"
+     sizes="(max-width: 1024px) 700px,
+            300px"
+     src="{{ large_image }}" alt="Image of Board" loading="lazy">

_includes/downloads/feed_board_image.html

@@ -17,7 +17,7 @@
   <item>
     <title>{{ board.name }}</title>
     <link>{{ board.url | absolute_url }}</link>
-    <description><![CDATA[ {% include downloads/feed_board_image.html board_image=board.board_image %}<p>By {{ board.manufacturer }}</p> {{ board.content }} ]]></description>
+    <description><![CDATA[ {% include downloads/board_image.html board_image=board.board_image %}<p>By {{ board.manufacturer }}</p> {{ board.content }} ]]></description>
     {% if board.blinka %}
     <category>Blinka</category>
     {% else %}