chore: added pnpm-deduplicate linting (#74)

Author: JoshuaKGoldberg

.github/workflows/packages.yml

@@ -0,0 +1,15 @@
+name: Lint Packages
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  package:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: ./.github/actions/prepare
+      - run: pnpm lint:packages

package.json

@@ -22,6 +22,7 @@
 		"markdownlint-cli": "^0.32.2",
 		"npm-package-json-lint": "^6.3.0",
 		"npm-package-json-lint-config-default": "^5.0.0",
+		"pnpm-deduplicate": "^0.4.0",
 		"prettier": "^2.7.1",
 		"semantic-release": "^19.0.5",
 		"ts-prune": "^0.10.3",
@@ -45,6 +46,7 @@
 		"lint": "npx eslint . --max-warnings 0 --report-unused-disable-directives",
 		"lint:md": "npx markdownlint \"**/*.md\" \".github/**/*.md\"",
 		"lint:package": "npmPkgJsonLint .",
+		"lint:packages": "pnpm-deduplicate --list",
 		"lint:prune": "ts-prune",
 		"lint:spelling": "cspell \"**\" \".github/**/*\"",
 		"prepare": "husky install",