image: allow the image to by auto-loaded by animation (#5139)

tests/test8.yaml

@@ -92,3 +92,13 @@ sensor:
       name: "Loop Time"
     psram:
       name: "PSRAM Free"
+
+# Purposely test that `animation:` does auto-load `image:`
+# Keep the `image:` undefined.
+# image:
+
+animation:
+  - id: rgb565_animation
+    file: pnglogo.png
+    type: RGB565
+    use_transparency: no