Add grammar-test script

Author: fpseverino

package.json

@@ -1682,7 +1682,8 @@
     "pretest": "npm run compile-tests",
     "soundness": "scripts/soundness.sh",
     "check-package-json": "tsx ./scripts/check_package_json.ts",
-    "test": "vscode-test",
+    "test": "vscode-test && npm run grammar-test",
+    "grammar-test": "vscode-tmgrammar-test 'test/unit-tests/**/*.test.swift.gyb' -g test/unit-tests/syntaxes/swift.tmLanguage.json -g test/unit-tests/syntaxes/MagicPython.tmLanguage.json",
     "integration-test": "npm test -- --label integrationTests",
     "unit-test": "npm test -- --label unitTests",
     "coverage": "npm test -- --coverage",