[FIX] "Open_thread" English tooltip correction

[aKn1ghtOut]

Checklist

• I have read the Contributing Guide
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Proposed changes (including videos or screenshots)

Remove unnecessary spaces from the translation key, and added English translation value for the key.

Issue(s)

Closes #20145

Steps to test or reproduce

1. Make a thread in a channel
2. Mouse over blue thread link in channel
3. Look at tooltip

Further comments