BAU: Bump alphagov/di-devplatform-upload-action-ecr from 1.0.3 to 1.0.4

Bumps [alphagov/di-devplatform-upload-action-ecr](https://github.com/alphagov/di-devplatform-upload-action-ecr) from 1.0.3 to 1.0.4.
- [Release notes](https://github.com/alphagov/di-devplatform-upload-action-ecr/releases)
- [Commits](alphagov/di-devplatform-upload-action-ecr@1.0.3...1.0.4)

---
updated-dependencies:
- dependency-name: alphagov/di-devplatform-upload-action-ecr
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/post-merge-deploy.yaml

@@ -29,7 +29,7 @@ jobs:
           password: ${{ secrets.DYNATRACE_PAAS_TOKEN }}
 
       - name: "Push signed image to ECR, updated SAM template with image then upload it to the S3 Artifact Bucket"
-        uses: alphagov/[email protected].3
+        uses: alphagov/[email protected].4
         with:
           artifact-bucket-name: ${{ secrets[format('{0}_{1}', matrix.environment, 'ARTIFACT_BUCKET')] }}
           container-sign-kms-key-arn: ${{ secrets[format('{0}_{1}', matrix.environment, 'CONTAINER_SIGN_KMS_KEY')] }}