actions: add an example for workflow-dispatch

/repos/{owner}/{repo}/actions/workflows/{workflowname}/dispatches

* fails if the required inputs are not provided
* sets defaults to inputs that are not provided

The type of inputs are only used for building the web UI interface,
not for validation. All values are strings.

actions/actions.sh

@@ -118,5 +118,11 @@ function test_actions() {
                 run actions_verify_example $example
             done
         fi
+
+        if dpkg --compare-versions $version ge 8.0 ; then
+            for example in workflow-dispatch ; do
+                run actions_verify_example $example
+            done
+        fi
     done
 }