Don't send device list updates upon registration

[S7evinK]

Fixes #3273

As we otherwise send down device list updates which are merely useful for the user and causes tests to be flakey:

❌ TestPushSync/Adding_a_push_rule_wakes_up_an_incremental_/sync (10ms)
      push_test.go:57: no pushrules found in sync response: {"next_batch":"s0_0_0_0_0_1_1_0_1","device_lists":{"changed":["@user-1:hs1"]}}

What this does: If a PerformDeviceCreation request is coming from registering an account, it does not send device list updates, as they are merely useful (no joined rooms, no one to inform) . In all other cases, the behavior is unchanged and device list updates are sent as usual.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (bebf701) 65.33% compared to head (4494a29) 65.28%.

Files	Patch %	Lines
userapi/internal/key_api.go	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3307      +/-   ##
==========================================
- Coverage   65.33%   65.28%   -0.05%     
==========================================
  Files         509      509              
  Lines       57488    57493       +5     
==========================================
- Hits        37560    37536      -24     
- Misses      16028    16052      +24     
- Partials     3900     3905       +5     

Flag	Coverage Δ
unittests	50.01% <76.92%> (-0.05%)	⬇️

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[S7evinK]

Also sneakily changes the project coverage threshold to 0.1%, as it is quite annoying to have CI failing just because a nightly run had slightly higher coverage.