AVM: Set proper costs for json_ref

[jannotti]

Made from Jacob's branch to fix a lint error while he's out.

[codecov]

Codecov Report

Merging #4096 (4da6b6f) into master (7147d01) will increase coverage by 0.01%.
The diff coverage is 84.37%.

@@            Coverage Diff             @@
##           master    #4096      +/-   ##
==========================================
+ Coverage   54.49%   54.50%   +0.01%     
==========================================
  Files         390      390              
  Lines       48620    48621       +1     
==========================================
+ Hits        26497    26503       +6     
+ Misses      19902    19891      -11     
- Partials     2221     2227       +6     

Impacted Files	Coverage Δ
data/transactions/logic/opcodes.go	83.76% <50.00%> (-1.11%)	⬇️
data/transactions/logic/eval.go	89.82% <95.45%> (+0.21%)	⬆️
data/transactions/logic/doc.go	61.53% <100.00%> (+1.53%)	⬆️
ledger/roundlru.go	90.56% <0.00%> (-5.67%)	⬇️
ledger/blockqueue.go	82.18% <0.00%> (-2.88%)	⬇️
ledger/tracker.go	74.45% <0.00%> (-2.17%)	⬇️
ledger/acctupdates.go	68.77% <0.00%> (-1.06%)	⬇️
network/wsNetwork.go	65.27% <0.00%> (+0.28%)	⬆️
network/wsPeer.go	68.76% <0.00%> (+0.54%)	⬆️
catchup/service.go	68.88% <0.00%> (+0.74%)	⬆️
... and 2 more

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