Fix version filter for beta releases

<a href="https://play.google.com/store/apps/details?id=net.thunderbird.android&referrer=utm_campaign%3Dandroid_metadata%26utm_medium%3Dweb%26utm_source%3Dgithub.com%26utm_content%3Dbadge" target="_blank"><img src="./docs/assets/get-it-on-play.png" alt="Get it on Google Play" height="28"></a>

<a href="https://f-droid.org/packages/net.thunderbird.android"><img src="./docs/assets/get-it-on-fdroid.png" alt="Get it on F-Droid" height="28"></a>

[![Latest release](https://img.shields.io/github/release/thunderbird/thunderbird-android.svg?style=for-the-badge&filter=THUNDERBIRD_*&logo=thunderbird)](https://github.com/thunderbird/thunderbird-android/releases/latest)

[![Latest beta release](https://img.shields.io/github/v/release/thunderbird/thunderbird-android.svg?include_prereleases&style=for-the-badge&label=beta&filter=THUNDERBIRD_*&logo=thunderbird)](https://github.com/thunderbird/thunderbird-android/releases)

[![Latest beta release](https://img.shields.io/github/release/thunderbird/thunderbird-android.svg?include_prereleases&style=for-the-badge&label=beta&filter=THUNDERBIRD_*b*&logo=thunderbird)](https://github.com/thunderbird/thunderbird-android/releases)

Thunderbird for Android is a powerful, privacy-focused email app. Effortlessly manage multiple email accounts from one app, with a Unified Inbox option for maximum productivity. Built on open-source technology and supported by a dedicated team of developers alongside a global community of volunteers, Thunderbird never treats your private data as a product.