Run ECR on push to dev & master (#244)

### Description
<!-- Describe what change this PR is implementing -->

Prevent building an image for each PR... just build the image for dev,
master branches & hotfix, release PRs.

### Types of Changes
<!--- What types of changes does your code introduce? -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Dependency upgrade (A change in substrate or any 3rd party crate
version)

### Migrations and Hooks
<!--- Check the following box with an x if the following applies: -->
- [ ] This change requires a runtime migration.
- [ ] Modifies `on_initialize`
- [ ] Modifies `on_finalize`

### Checklist
<!--- All boxes need to be checked. Follow this checklist before
requiring PR review -->
- [ ] Change has been tested locally.
- [ ] Change adds / updates tests.
- [ ] Changelog doc updated.

.github/workflows/ecr.yaml

@@ -1,10 +1,13 @@
 name: ECR
 
 on:
-  pull_request:
+  push:
     branches:
       - dev
+      - staging
       - master
+  pull_request:
+    branches:
       - 'release/**'
       - 'hotfix/**'
     types: