WidgetDriver: Add io.element.call.encryption_keys to-device capability.

[toger5]

This needs to be part of the send/read capabilities so that to-device keys can be used.

Blocked by (depends on): #4963

• Public API changes documented in changelogs (optional)

Signed-off-by:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.83%. Comparing base (9fbb9cb) to head (1dd17c0).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4990      +/-   ##
==========================================
- Coverage   85.83%   85.83%   -0.01%     
==========================================
  Files         325      325              
  Lines       35848    35848              
==========================================
- Hits        30771    30769       -2     
- Misses       5077     5079       +2     

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[toger5]

now part of: #4963