fix: temporarily use the pip install method for the setup-matrix-synapse action

[bnjbvr]

Until michaelkaye/setup-matrix-synapse#95 is properly resolved.

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.01% ⚠️

Comparison is base (5497a8d) 77.11% compared to head (c75ce9f) 77.10%.
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2431      +/-   ##
==========================================
- Coverage   77.11%   77.10%   -0.01%     
==========================================
  Files         181      182       +1     
  Lines       19166    19178      +12     
==========================================
+ Hits        14779    14787       +8     
- Misses       4387     4391       +4     

Files Changed	Coverage Δ
...matrix-sdk-ui/src/room_list_service/filters/mod.rs	100.00% <ø> (ø)
...list_service/filters/normalized_match_room_name.rs	66.66% <66.66%> (ø)

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