Add missed spec version 1.12 in the sdf_descriptions target

This also updates the default versions in root.sdf files

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Author: azeey

sdf/1.11/root.sdf

@@ -1,7 +1,7 @@
 <element name="sdf" required="1">
   <description>SDFormat base element that can include one model, actor, light, or worlds. A user of multiple worlds could run parallel instances of simulation, or offer selection of a world at runtime.</description>
 
-  <attribute name="version" type="string" default="1.10" required="1">
+  <attribute name="version" type="string" default="1.11" required="1">
     <description>
         Version number of the SDFormat specification, consisting of major
         and minor versions delimited by a `.` character.

sdf/1.12/root.sdf

@@ -1,7 +1,7 @@
 <element name="sdf" required="1">
   <description>SDFormat base element that can include one model, actor, light, or worlds. A user of multiple worlds could run parallel instances of simulation, or offer selection of a world at runtime.</description>
 
-  <attribute name="version" type="string" default="1.10" required="1">
+  <attribute name="version" type="string" default="1.12" required="1">
     <description>
         Version number of the SDFormat specification, consisting of major
         and minor versions delimited by a `.` character.

sdf/CMakeLists.txt

@@ -32,7 +32,7 @@ execute_process(
 if (GZ_PROGRAM)
 
   # Update this list as new sdformat spec versions are added.
-  set(sdf_desc_versions 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11)
+  set(sdf_desc_versions 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12)
 
   set(description_targets)
   foreach(desc_ver ${sdf_desc_versions})