chore: update showcase version for sequence tests

[noahdietz]

This updates the version of Showcase used for generation in CI to v0.12.0 and adds a test for the new SequenceService to assert the basic retry attempt logic and timeout-backoff behavior works as implemented.

[noahdietz]

I'm not really sure why the ruby tests are failing with TypeError: Sequence is not a module - my hunch is that the service is named SequenceService and there is a message named Sequence and somehow this results in a naming conflict.

Not really sure what to do about that. We've migrated everything to gapic-generator-ruby, maybe we shouldn't make the tests required?

[vam-google]

LGTM with a a few minor comments.
Let's ask @viacheslav-rostovtsev he things about ruby failures?

[noahdietz]

Just spoke to dazuma and he said that naming collisions are definitely possible, real cases in cloud libs were worked around with synthtool, and were ultimately fixed with the microgenerator. I guess I should do something to exclude this proto from Ruby generation in this CI.

[noahdietz]

Fixed it by breaking out ruby generation, and before generating it, I moved the offending proto out of the target directory and remove the service from the 1P yaml. Hacky, but really the only way to exclude this proto from ruby showcase gen.

[codecov]

Codecov Report

Merging #3268 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3268   +/-   ##
=========================================
  Coverage     87.12%   87.12%           
  Complexity     6080     6080           
=========================================
  Files           494      494           
  Lines         24060    24060           
  Branches       2613     2613           
=========================================
  Hits          20962    20962           
  Misses         2236     2236           
  Partials        862      862           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dc019bd...8c653b5. Read the comment docs.