Fix sensor/user element's attribute defaults

PiperOrigin-RevId: 514787631
Change-Id: Ibc1733a2c6bd302acfdc00f0db4044b0c3677c58

Author: DeepMind

dm_control/mjcf/schema.xml

@@ -2168,10 +2168,10 @@
             <attribute name="noise" type="float"/>
             <attribute name="cutoff" type="float"/>
             <attribute name="user" type="array" array_type="float"/>
-            <attribute name="objtype" type="keyword" required="true" valid_values="body joint geom site camera light mesh skin hfield texture material equality tendon actuator sensor numeric text tuple contact keyframe"/>
-            <attribute name="objname" type="reference" required="true" reference_namespace="attrib:objtype"/>
-            <attribute name="datatype" type="keyword" required="true" valid_values="real positive axis quaternion"/>
-            <attribute name="needstage" type="keyword" required="true" valid_values="pos vel acc"/>
+            <attribute name="objtype" type="keyword" valid_values="body joint geom site camera light mesh skin hfield texture material equality tendon actuator sensor numeric text tuple contact keyframe"/>
+            <attribute name="objname" type="reference" reference_namespace="attrib:objtype"/>
+            <attribute name="datatype" type="keyword" valid_values="real positive axis quaternion"/>
+            <attribute name="needstage" type="keyword" valid_values="pos vel acc"/>
             <attribute name="dim" type="int" required="true"/>
           </attributes>
         </element>

dm_control/mjcf/test_assets/test_model.xml

@@ -1,4 +1,5 @@
 <mujoco model="test">
+  <size memory="1024"/>
   <compiler texturedir="textures"/>
   <asset>
     <texture name="texture" type="cube" file="deepmind.png"/>
@@ -42,4 +43,7 @@
     <velocity name="b_0_0" joint="b_0_0"/>
     <velocity name="b_1_0" joint="b_1_0"/>
   </actuator>
+  <sensor>
+    <user name="dummy" dim="1" user="0 1 0 1" />
+  </sensor>
 </mujoco>