ci: adjust PR syntax for code coverage, only on merged PRs to `develo…

…p` (#771)

* ci: adjust PR syntax for code coverage, only on merged PRs to `develop`

* ci: adjust nodejs heap memory

.github/workflows/coverage.yml

@@ -4,14 +4,21 @@
 
 name: Solidity Code coverage
 
+env:
+  # 4GB of memory to prevent max heap size error when running code coverage
+  NODE_OPTIONS: "--max_old_space_size=4096"
+
 on:
-  push:
+  pull_request:
     branches:
       - "develop"
+    types:
+      - closed
 
 jobs:
   coverage:
     runs-on: ubuntu-latest
+    if: github.event.pull_request.merged == true
     steps:
       - uses: actions/checkout@v3