Do not warn users if a workflow cannot be read

This will still send a LintFailed message status report.

lib/actions-util.js

@@ -294,7 +294,6 @@ async function getWorkflow() {
         return yaml.safeLoad(fs.readFileSync(absolutePath, "utf-8"));
     }
     catch (e) {
-        core.warning(`Could not read workflow: ${e.toString()}`);
         return undefined;
     }
 }