Patch: for when artifactName is empty string.

The Error we are seeing when the action is run before this change:
Validation Failed: {"resource":"Deployment","code":"custom","field":"task","message":"task is too short (minimum is 1 character)"}

Fixing oversight from this change:
#46

src/index.ts

@@ -106,7 +106,7 @@ const createDeployment = async () => {
     const response = await octokit.repos.createDeployment({
         ...context.repo,
         ref: githubDeploymentRef,
-        task: artifactName,
+        task: artifactName || undefined,
         required_contexts: [],
         githubEnvironmentName,
         auto_merge: false,