Improve message in ob_parbone() about the missing Parent Bone

- lower to warning (might be debatable, but this is not really
malfunctioning and e.g. constraints/modifiers dont spit out errors if
targets are not specified)
- clarify _what_ of the two actualy does not exist

ref. T91101

Maniphest Tasks: T91101

Differential Revision: https://developer.blender.org/D12389

source/blender/blenkernel/intern/object.c

@@ -3307,8 +3307,8 @@ static void ob_parbone(Object *ob, Object *par, float r_mat[4][4])
   /* Make sure the bone is still valid */
   bPoseChannel *pchan = BKE_pose_channel_find_name(par->pose, ob->parsubstr);
   if (!pchan || !pchan->bone) {
-    CLOG_ERROR(
-        &LOG, "Object %s with Bone parent: bone %s doesn't exist", ob->id.name + 2, ob->parsubstr);
+    CLOG_WARN(
+        &LOG, "Parent Bone: '%s' for Object: '%s' doesn't exist", ob->parsubstr, ob->id.name + 2);
     unit_m4(r_mat);
     return;
   }