eth/client: add test for tx_succeeded?

[q9f]

after #173

[codecov-commenter]

Codecov Report

Merging #183 (55de840) into main (1633ed0) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #183      +/-   ##
==========================================
+ Coverage   99.70%   99.75%   +0.04%     
==========================================
  Files          70       70              
  Lines        4077     4086       +9     
==========================================
+ Hits         4065     4076      +11     
+ Misses         12       10       -2     

Impacted Files	Coverage Δ
lib/eth/client.rb	100.00% <100.00%> (+1.25%)	⬆️
spec/eth/client_spec.rb	100.00% <100.00%> (ø)

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[kurotaky]

Thanks!