force yarn 1.21.1 until we can handle invalid output of 1.22.0 (#56914)

package.json

@@ -486,6 +486,6 @@
   },
   "engines": {
     "node": "10.18.0",
-    "yarn": "^1.21.1"
+    "yarn": "1.21.1"
   }
 }

src/dev/ci_setup/setup_env.sh

@@ -108,8 +108,7 @@ if [[ "$installNode" == "true" || ! $(which yarn) ]]; then
   ###
   ### downloading yarn
   ###
-  yarnVersion="$(node -e "console.log(String(require('./package.json').engines.yarn || '').replace(/^[^\d]+/,''))")"
-  npm install -g "yarn@^${yarnVersion}"
+  npm install -g "yarn@$(node -e "console.log(require('./package.json').engines.yarn)")"
 fi
 
 ###

x-pack/package.json

@@ -351,7 +351,7 @@
     "xregexp": "4.2.4"
   },
   "engines": {
-    "yarn": "^1.21.1"
+    "yarn": "1.21.1"
   },
   "workspaces": {
     "nohoist": [