Switch optimised video uploads to use 720p

[pixlwave]

As decided in element-hq/element-meta#2543 (comment)

[github-actions]

	Warnings
⚠️	Some of the commits are missing ticket numbers. Please consider squashing all commits that don't have a tracking number.

Generated by 🚫 Danger Swift against 3019057

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.95%. Comparing base (a583892) to head (3019057).
Report is 2 commits behind head on develop.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3462      +/-   ##
===========================================
+ Coverage    77.89%   77.95%   +0.06%     
===========================================
  Files          742      742              
  Lines        61242    61242              
===========================================
+ Hits         47705    47742      +37     
+ Misses       13537    13500      -37     

Flag	Coverage Δ
unittests	69.48% <100.00%> (+0.06%)	⬆️

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