Fix rn-tester convenience scripts (#49401)

Summary:
Pull Request resolved: #49401

These scripts erroneously invoked `npm`, requiring `--` to forward args.

Discovered while testing #49353.

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D69594024

fbshipit-source-id: a6e8cccaf994f1472b51155d36a49ed17cd291dc

Author: huntie

package.json

@@ -5,7 +5,7 @@
   "license": "MIT",
   "packageManager": "yarn@1.22.22",
   "scripts": {
-    "android": "cd packages/rn-tester && npm run android",
+    "android": "yarn --cwd packages/rn-tester android",
     "build-android": "./gradlew :packages:react-native:ReactAndroid:build",
     "build": "node ./scripts/build/build.js",
     "clang-format": "clang-format -i --glob=*/**/*.{h,cpp,m,mm}",
@@ -14,14 +14,14 @@
     "flow": "flow",
     "format-check": "prettier --list-different \"./**/*.{js,md,yml,ts,tsx}\"",
     "format": "npm run prettier && npm run clang-format",
-    "featureflags": "cd packages/react-native && yarn featureflags",
+    "featureflags": "yarn --cwd packages/react-native featureflags",
     "lint-ci": "./scripts/circleci/analyze_code.sh && yarn shellcheck",
     "lint-java": "node ./scripts/lint-java.js",
     "lint": "eslint .",
     "prettier": "prettier --write \"./**/*.{js,md,yml,ts,tsx}\"",
     "print-packages": "node ./scripts/monorepo/print",
     "shellcheck": "./scripts/circleci/analyze_scripts.sh",
-    "start": "cd packages/rn-tester && npm run start",
+    "start": "yarn --cwd packages/rn-tester start",
     "set-version": "node ./scripts/releases/set-version.js",
     "test-android": "./gradlew :packages:react-native:ReactAndroid:test",
     "test-ci": "jest --maxWorkers=2 --ci --reporters=\"default\" --reporters=\"jest-junit\"",