Update Testing United 2026 listing

[Copilot]

Conference/Workshop Details

• Name, Location, Date(s), Website URL and Status are required
• X / Twitter is Optional
• Location should be City + Country or Online
• Status can include information about registration, pricing, calls for proposals and can include links to all the above.

Checklist

• I have added the conference/workshop to the correct YAML file (_data/current.yml or _data/past.yml)
• The entry includes name, location, date(s), url and accurate status
• The entry is in chronological order (soonest to furtherest away)
• If there are any special characters in the name field (: or ; or '), the name must be in quotes (")
• I have checked for duplicates to avoid listing the same event twice
• Build runs successfully

Additional context

The event listing for Testing United was missing the year, making the current entry ambiguous in the conference list.

• Updated the current conference entry in _data/current.yml to Testing United 2026
• Kept the event consistent with the repository’s naming convention for annual conference entries

• Fixes Testing United #925