txsource/queries: increase the odds of querying the latest height

[ptrus]

To test things like: #2786

Probably shouldn't have removed this from the initial queries PR in the first place :-)

[codecov]

Codecov Report

Merging #2787 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2787      +/-   ##
==========================================
+ Coverage   62.85%   62.88%   +0.02%     
==========================================
  Files         389      389              
  Lines       37080    37084       +4     
==========================================
+ Hits        23308    23321      +13     
+ Misses      10807    10789      -18     
- Partials     2965     2974       +9     

Impacted Files	Coverage Δ
.../oasis-node/cmd/debug/txsource/workload/queries.go	57.54% <100.00%> (+0.60%)	⬆️
...oasis-node/cmd/debug/txsource/workload/transfer.go	0.00% <0.00%> (-63.81%)	⬇️
go/worker/common/host/interface.go	38.46% <0.00%> (-15.39%)	⬇️
...ompute/txnscheduler/algorithm/batching/batching.go	78.66% <0.00%> (-6.67%)	⬇️
go/common/grpc/auth/auth.go	88.88% <0.00%> (-5.56%)	⬇️
go/worker/compute/txnscheduler/committee/node.go	62.34% <0.00%> (-4.02%)	⬇️
go/oasis-node/cmd/debug/storage/storage.go	45.08% <0.00%> (-3.47%)	⬇️
go/storage/metrics.go	81.52% <0.00%> (-3.27%)	⬇️
go/worker/common/host/protocol/protocol.go	65.67% <0.00%> (-2.99%)	⬇️
go/storage/database/database.go	77.27% <0.00%> (-1.82%)	⬇️
... and 13 more

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