Fix return license

Author: kuler90

action.yml

@@ -20,7 +20,6 @@ runs:
   using: node12
   main: src/activate-license.js
   post: src/return-license.js
-  post-if: inputs.unity-serial != ''
 branding:
   icon: unlock
   color: gray-dark

src/return-license.js

@@ -7,7 +7,9 @@ async function run() {
         if (!unityPath) {
             throw new Error('unity path not found');
         }
-        await unity.returnLicense(unityPath);
+        if (core.getInput('unity-serial')) {
+            await unity.returnLicense(unityPath);
+        }
     } catch (error) {
         core.setFailed(error.message);
     }