Fix view.set() for parents (SYN-5392)

[vEpiphyte]

No description provided.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.10 ⚠️

Comparison is base (b91e8b5) 97.29% compared to head (ee40dce) 97.19%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3131      +/-   ##
==========================================
- Coverage   97.29%   97.19%   -0.10%     
==========================================
  Files         222      222              
  Lines       44200    44200              
==========================================
- Hits        43006    42962      -44     
- Misses       1194     1238      +44     

Flag	Coverage Δ
linux	97.19% <100.00%> (ø)
linux_replay	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
synapse/lib/view.py	97.04% <100.00%> (-0.33%)	⬇️

... and 8 files with indirect coverage changes

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