fix: Escape brace of dumped JSON for index err message

[congqixia]

Related to #37503

[sre-ci-robot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.30%. Comparing base (7cfd609) to head (dfa3f63).
Report is 19 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #37504       +/-   ##
===========================================
- Coverage   83.23%   67.30%   -15.94%     
===========================================
  Files        1015      290      -725     
  Lines      157697    25400   -132297     
===========================================
- Hits       131260    17095   -114165     
+ Misses      21228     8305    -12923     
+ Partials     5209        0     -5209     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	67.30% <48.52%> (∅)
Go	∅ <ø> (∅)

Files with missing lines	Coverage Δ
internal/core/src/index/VectorMemIndex.cpp	64.82% <100.00%> (ø)

... and 1304 files with indirect coverage changes

[aoiasd]

/lgtm