Switch to the Coveralls Action (#29478)

This is the official way of using Coveralls with Actions. Also this brings back Coveralls for PRs.

package.json

@@ -65,7 +65,6 @@
     "js-test-integration": "rollup --config js/tests/integration/rollup.bundle.js",
     "js-test-cloud": "cross-env BROWSER=true npm run js-test-karma",
     "lint": "npm-run-all --parallel js-lint css-lint",
-    "coveralls": "shx cat js/coverage/lcov.info | coveralls",
     "docs": "npm-run-all css-docs js-docs docs-compile docs-lint",
     "docs-compile": "bundle exec jekyll build",
     "docs-production": "cross-env JEKYLL_ENV=production npm run docs-compile",
@@ -114,7 +113,6 @@
     "broken-link-checker": "^0.7.8",
     "bundlesize": "^0.18.0",
     "clean-css-cli": "^4.3.0",
-    "coveralls": "^3.0.7",
     "cross-env": "^5.2.1",
     "eslint": "^5.16.0",
     "find-unused-sass-variables": "^0.6.0",