fix: remove incorrect prepare workflow call in build-and-push-image.yml (#1336)

follow-up to #1334

The build-and-push-image workflow was incorrectly calling the prepare.yml
as a step action instead of using it as a reusable workflow. This caused
the error "Can't find 'action.yml', 'action.yaml' or 'Dockerfile' under
.github/workflows/prepare.yml".

Example: https://github.com/kubeflow/model-registry/actions/runs/16379707719/job/46288348593

The prepare job is already correctly called at the top of the jobs section,
so the duplicate call in the steps was unnecessary and likely the cause
of the failure.

Signed-off-by: Matteo Mortari <[email protected]>

Author: tarilabs

.github/workflows/build-and-push-image.yml

@@ -47,7 +47,6 @@ jobs:
         if: env.BUILD_CONTEXT == 'tag'
         run: |
           echo "VERSION=${{ github.ref_name }}" >> $GITHUB_ENV
-      - uses: ./.github/workflows/prepare.yml
       - name: Build and Push Image
         shell: bash
         run: ./scripts/build_deploy.sh