fix: RelationalLinkedChunk handles Update::Clear

[Hywan]

What the title says.

[stefanceriu]

👍

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.06%. Comparing base (912b121) to head (b90ba0e).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/matrix-sdk-common/src/linked_chunk/relational.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4319      +/-   ##
==========================================
- Coverage   85.07%   85.06%   -0.02%     
==========================================
  Files         274      275       +1     
  Lines       30204    30314     +110     
==========================================
+ Hits        25697    25786      +89     
- Misses       4507     4528      +21     

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