Remove duplicate sign in nightly-test-release.yaml

We are performing sign process as a part of the `release.yaml` workflow, so this was added by mistake.

.github/workflows/nightly-test-release.yaml

@@ -56,30 +56,6 @@ jobs:
       secret_registry: ${{ matrix.secret_registry }}
     secrets: inherit
 
-  sign:
-    runs-on: ubuntu-latest
-    needs: [build-push-services]
-    permissions:
-      actions: read
-      id-token: write
-      packages: write
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-          ref: ${{ inputs.tag }}
-      - name: Sign image with cosign
-        uses: ./.github/workflows/release_sign
-        with:
-          image: ${{ vars[inputs.image] }}
-          digest: ${{ needs.build.outputs.digest }}
-          identity: https://github.com/${{ inputs.org }}/turtles/.github/workflows/nightly-test-release.yml@${{ github.ref }}
-          oids-issuer: https://token.actions.githubusercontent.com
-          registry: ${{ inputs.secret_registry && secrets[inputs.registry] || inputs.registry }}
-          username: ${{ inputs.secret_registry && secrets[inputs.username] || inputs.username }}
-          password: ${{ secrets[inputs.password] }}
-
   release:
     name: Create helm release
     needs: [sign]