Index: .npmrc
===================================================================
--- .npmrc	(revision 54121)
+++ .npmrc	(working copy)
@@ -1 +1,2 @@
 save-exact = true
+engine-strict = true
Index: package.json
===================================================================
--- package.json	(revision 54121)
+++ package.json	(working copy)
@@ -8,7 +8,7 @@
 	},
 	"engines": {
 		"node": ">=14.15.0",
-		"npm": ">=6.14.8"
+		"npm": ">=6.14.8 <7"
 	},
 	"author": "The WordPress Contributors",
 	"license": "GPL-2.0-or-later",