Update dependency preact-render-to-string to v5.1.21

Author: renovate[bot]

package.json

@@ -53,7 +53,7 @@
   "dependencies": {
     "@storybook/client-api": "6.4.19",
     "preact": "10.6.5",
-    "preact-render-to-string": "5.1.19",
+    "preact-render-to-string": "5.1.21",
     "react-dom": "17.0.2"
   },
   "publishConfig": {