ci: refactor workflow_dispath

Signed-off-by: Christina Sørensen <christina@cafkafk.com>

.github/workflows/flakehub-publish-tagged.yml

@@ -3,6 +3,11 @@ on:
     tags:
       - "v*.*.*"
   workflow_dispatch:
+    inputs:
+      tag:
+        description: The Git tag to use, for non-rolling releases. This must be the character `v` followed by a SemVer version, e.g. `v0.1.1`.
+        required: true
+
 jobs:
   publish:
     runs-on: "ubuntu-latest"