Add jammy rosdoc2 jobs as well. (#1037)

I couldn't figure out if there was a better solution than just doubling
the existing job. I marked the previous one as for Noble and the one I
just added for Humble as "jammy" I guess that when we introduce new
platforms we'd roll these forward or back based on what is currently
supported.

.github/workflows/ci.yaml

@@ -297,8 +297,8 @@ jobs:
           os_code_name: jammy
           repo: rcutils
 
-  ros2_doc:
-    name: ROS 2 Doc
+  ros2_doc_noble:
+    name: ROS 2 Doc (Noble)
     runs-on: ubuntu-20.04
     steps:
       - name: Check out project
@@ -314,6 +314,23 @@ jobs:
           repo: rcl
           output_directory: ws/docs_output
 
+  ros2_doc_jammy:
+    name: ROS 2 Doc (Jammy)
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Check out project
+        uses: actions/checkout@v2
+      - name: Install dependencies
+        uses: ./.github/actions/setup
+      - name: Run job
+        uses: ./.github/actions/doc
+        with:
+          config_url: https://raw.githubusercontent.com/ros2/ros_buildfarm_config/ros2/index.yaml
+          ros_distro: humble
+          os_code_name: jammy
+          repo: rcl
+          output_directory: ws/docs_output
+
   ros2_prerelease:
     name: ROS 2 Prerelease
     runs-on: ubuntu-20.04