Lock notification says "locked" even when the discussion is unlocked

## Bug Report

**Current Behavior**

Currently when you lock a discussion the web notification that is generated says "{user} locked".

The text is the same even if the admin/mod actually unlocked the discussion.

https://github.com/flarum/lock/blob/c4383c318899fce6d5e7c936695edbe5f7f49c88/locale/en.yml#L28

**Steps to Reproduce**

1. Lock a discussion
2. Notice the text of the notification delivered to the discussion author

**Expected Behavior**

I think the notification text should distinguish between locked/unlocked.

**Environment**
- Flarum version: 1.2.0

**Possible Solution**

The notification data should include whether the action is lock or unlock, in order to expose that information to the client.