Fix warning: unused variable ‘init’ [-Wunused-variable]

[mloskot]

Pedantic avoidance of

../../libs/json/test/value_ref.cpp:177:29: error: expected primary-expression before ‘init’
  177 |             (void)init_list init =
      |                             ^~~~

[codecov]

Codecov Report

Merging #49 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #49   +/-   ##
========================================
  Coverage    99.09%   99.09%           
========================================
  Files           57       57           
  Lines         4854     4854           
========================================
  Hits          4810     4810           
  Misses          44       44

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[vinniefalco]

Thanks!