Add release notes for 7.21

_locales/en/messages.json

@@ -7495,5 +7495,9 @@
   "icu:WhatsNew__v7.20--1": {
     "messageformat": "This release also improves the performance of link preview generation and fixes a bug that caused the Settings window to briefly flash a lovely shade of ultramarine whenever it was closed (instead of just closing right away).",
     "description": "Release notes for version 7.20, part 2"
+  },
+  "icu:WhatsNew__v7.21--0": {
+    "messageformat": "Everyone loves a good story, and we could tell you the tale of a bug that sometimes caused the progress bar to freeze right in the middle of watching a good story — but that bug's adventure already has a happy ending because we fixed it in this release.",
+    "description": "Release notes for version 7.21"
   }
 }

ts/components/WhatsNewModal.tsx

@@ -42,10 +42,7 @@ export function WhatsNewModal({
   const releaseNotes: ReleaseNotesType = {
     date: new Date(window.getBuildCreation?.() || Date.now()),
     version: window.getVersion?.(),
-    features: [
-      <I18n i18n={i18n} id="icu:WhatsNew__v7.20--0" />,
-      <I18n i18n={i18n} id="icu:WhatsNew__v7.20--1" />,
-    ],
+    features: [<I18n i18n={i18n} id="icu:WhatsNew__v7.21--0" />],
   };
 
   if (releaseNotes.features.length === 1 && !releaseNotes.header) {