fix(ci): add on clause for the custom-release workflow

Author: glihm

.github/workflows/custom-release.yml

@@ -7,4 +7,11 @@
 # custom is a descriptive name for the release and X is the version number.
 #
 # gh workflow run custom-release.yml --ref feat/your-branch -f preview=v1.7.0-custom.1
-#
+#
+on:
+  workflow_dispatch:
+    inputs:
+      preview:
+        description: Useless just to have valid workflow file
+        required: true
+        type: string