Bump version to 3.0.0-beta.21

- Update the Android version name for the beta.21 prerelease
- Keep the release branch ready for the tagged Play build

🤖 Auto-generated

Author: OwenMcGirr

app/build.gradle.kts

@@ -17,7 +17,7 @@ android {
         minSdk = 29
         targetSdk = 36
         versionCode = gitVersionCode()
-        versionName = "3.0.0-beta.20"
+        versionName = "3.0.0-beta.21"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables {