Fix T76717: Set Rotation Mode Incorrectly Recalculates Bone Rotation In Pose Mode

The issue was that we didn't convert the current rotational values.
We simply just switched mode without doing any data conversions.

source/blender/editors/armature/pose_edit.c

@@ -665,6 +665,11 @@ static int pose_bone_rotmode_exec(bContext *C, wmOperator *op)
 
   /* set rotation mode of selected bones  */
   CTX_DATA_BEGIN_WITH_ID (C, bPoseChannel *, pchan, selected_pose_bones, Object *, ob) {
+    /* use API Method for conversions... */
+    BKE_rotMode_change_values(
+        pchan->quat, pchan->eul, pchan->rotAxis, &pchan->rotAngle, pchan->rotmode, (short)mode);
+
+    /* finally, set the new rotation type */
     pchan->rotmode = mode;
 
     if (prev_ob != ob) {