renderer: never use linear downscaling on HDR sources

This logic regressed sometime in the move from mpv vo_gpu to libplacebo.

Fixes: mpv-player/mpv#11036
See-Also: mpv-player/mpv#4631

src/renderer.c

@@ -1875,12 +1875,10 @@ static bool pass_scale_main(struct pass_state *pass)
     if (params->disable_linear_scaling || fbofmt->component_depth[0] < 16)
         use_sigmoid = use_linear = false;
 
-    // Avoid sigmoidization for HDR content because it clips to [0,1]
-    if (pl_color_space_is_hdr(&img->color)) {
-        use_sigmoid = false;
-        if (fbofmt->type != PL_FMT_FLOAT)
-            use_linear = false; // linear HDR needs out-of-range signals
-    }
+    // Avoid sigmoidization for HDR content because it clips to [0,1], and
+    // linearization because it causes very nasty ringing artefacts.
+    if (pl_color_space_is_hdr(&img->color))
+        use_sigmoid = use_linear = false;
 
     if (!use_linear && img->color.transfer == PL_COLOR_TRC_LINEAR) {
         img->color.transfer = image->color.transfer;