Add missing gain type "affine" to general actuators.

PiperOrigin-RevId: 463605415
Change-Id: Ic01e6721f101d5b55b1a1cbbc347ffe8e07f3a86

Author: DeepMind

dm_control/mjcf/schema.xml

@@ -384,7 +384,7 @@
             <attribute name="cranklength" type="float"/>
             <attribute name="user" type="array" array_type="float"/>
             <attribute name="dyntype" type="keyword" valid_values="none integrator filter user"/>
-            <attribute name="gaintype" type="keyword" valid_values="fixed user"/>
+            <attribute name="gaintype" type="keyword" valid_values="fixed affine user"/>
             <attribute name="biastype" type="keyword" valid_values="none affine user"/>
             <attribute name="dynprm" type="array" array_type="float" array_size="10"/>
             <attribute name="gainprm" type="array" array_type="float" array_size="10"/>
@@ -668,7 +668,7 @@
                 <attribute name="cranklength" type="float"/>
                 <attribute name="user" type="array" array_type="float"/>
                 <attribute name="dyntype" type="keyword" valid_values="none integrator filter user"/>
-                <attribute name="gaintype" type="keyword" valid_values="fixed user"/>
+                <attribute name="gaintype" type="keyword" valid_values="fixed affine user"/>
                 <attribute name="biastype" type="keyword" valid_values="none affine user"/>
                 <attribute name="dynprm" type="array" array_type="float" array_size="10"/>
                 <attribute name="gainprm" type="array" array_type="float" array_size="10"/>
@@ -1504,7 +1504,7 @@
             <attribute name="slidersite" type="reference" reference_namespace="site"/>
             <attribute name="user" type="array" array_type="float"/>
             <attribute name="dyntype" type="keyword" valid_values="none integrator filter muscle user"/>
-            <attribute name="gaintype" type="keyword" valid_values="fixed muscle user"/>
+            <attribute name="gaintype" type="keyword" valid_values="fixed affine muscle user"/>
             <attribute name="biastype" type="keyword" valid_values="none affine muscle user"/>
             <attribute name="dynprm" type="array" array_type="float" array_size="10"/>
             <attribute name="gainprm" type="array" array_type="float" array_size="10"/>