allow strings for has_props

[tschaume]

fix for https://matsci.org/t/issue-with-search-mp-api-with-has-props/57147/2 @computron

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.37%. Comparing base (8197ba3) to head (18eff30).

Files	Patch %	Lines
mp_api/client/routes/materials/summary.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #930      +/-   ##
==========================================
- Coverage   67.38%   67.37%   -0.01%     
==========================================
  Files          49       49              
  Lines        2520     2526       +6     
==========================================
+ Hits         1698     1702       +4     
- Misses        822      824       +2     

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