Update dependency execa to v6

Author: renovate[bot]

package-lock.json

@@ -45,7 +45,7 @@
     "eslint-config-prettier": "8.3.0",
     "eslint-plugin-prettier": "4.0.0",
     "espree": "9.3.0",
-    "execa": "5.1.1",
+    "execa": "6.0.0",
     "fast-glob": "3.2.11",
     "gray-matter": "4.0.3",
     "gulp": "4.0.2",