Fix proxy camera conversion with PNG Alpha(RGBA) (#40446)

homeassistant/components/proxy/camera.py

@@ -77,6 +77,8 @@ def _precheck_image(image, opts):
     if imgfmt not in ("PNG", "JPEG"):
         _LOGGER.warning("Image is of unsupported type: %s", imgfmt)
         raise ValueError()
+    if not img.mode == "RGB":
+        img = img.convert("RGB")
     return img