ci: Use tag as version build arg

Author: PythonGermany

.github/workflows/publish-custom.yml

@@ -5,6 +5,7 @@ on:
     inputs:
       tag:
         description: Custom tag to publish
+        default: custom
       platforms:
         description: Platforms to publish to (comma separated list)
         default: linux/amd64
@@ -48,5 +49,5 @@ jobs:
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           build-args: |
-            VERSION=custom
+            VERSION=${{ inputs.tag }}
             COMMIT_HASH=${{ github.sha }}