chore: use 2.22 milestone labels

[david-allison]

https://github.com/ankidroid/Anki-Android/milestone/69 => 2.22

• Part of Fix milestone on early 2.22 PRs/issues #18830 (past issues/PRs aren't fixed, future ones will be)

See f84a1bc for 2.21 bump

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner