Merge pull request #1737 from alphagov/upgrade-yarn-to-v4

Upgrade Yarn to v4

Author: ryanb-gds

.gitignore

@@ -24,3 +24,9 @@
 /spec/reports
 
 /yarn-error.log
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions

.yarn/releases/yarn-4.0.2.cjs

@@ -0,0 +1,3 @@
+nodeLinker: node-modules
+
+yarnPath: .yarn/releases/yarn-4.0.2.cjs

.yarnrc.yml

@@ -44,5 +44,6 @@
   "resolutions": {
     "stylelint/strip-ansi": "6.0.1",
     "stylelint/string-width": "4.2.3"
-  }
+  },
+  "packageManager": "yarn@4.0.2"
 }