Allow to templatize schedule tag (#1)

Co-authored-by: CrazyMax <crazy-max@users.noreply.github.com>

src/main.ts

@@ -31,7 +31,7 @@ async function run() {
     core.startGroup(`Docker image version`);
     core.info(`${version}`);
     core.endGroup();
-    core.setOutput('version', version);
+    core.setOutput('version', version || '');
 
     const tags: Array<string> = meta.tags();
     core.startGroup(`Docker tags`);