Update timeline when members are synced

[jplatte]

… as it's not available when members for the room aren't synced.

Ready for testing.

[stefanceriu]

This seems to be working beautifully ElX side, nicely done 👏

[jplatte]

sigh coverage not running again.

[poljar]

Looks good.

[codecov]

Codecov Report

Base: 73.11% // Head: 72.85% // Decreases project coverage by -0.27% ⚠️

Coverage data is based on head (d8438a8) compared to base (d08606e).
Patch coverage: 38.82% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1406      +/-   ##
==========================================
- Coverage   73.11%   72.85%   -0.27%     
==========================================
  Files         121      121              
  Lines       13229    13282      +53     
==========================================
+ Hits         9673     9677       +4     
- Misses       3556     3605      +49     

Impacted Files	Coverage Δ
crates/matrix-sdk/src/room/timeline/mod.rs	82.73% <0.00%> (-0.60%)	⬇️
crates/matrix-sdk/src/room/timeline/inner.rs	66.17% <7.31%> (-10.55%)	⬇️
crates/matrix-sdk/src/room/timeline/event_item.rs	50.47% <29.41%> (-2.08%)	⬇️
...ates/matrix-sdk/src/room/timeline/event_handler.rs	69.09% <96.00%> (+0.09%)	⬆️
crates/matrix-sdk/src/room/common.rs	84.61% <100.00%> (ø)

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