Add failing test-unit-proto CI job

[aaronc]

ref: #6213

This adds a failing CI job for make test-unit-proto which runs unit tests against protobuf transactions.

This job is expected to fail until the critical path of #6213 is complete and is intended to provide developers working on #6213 feedback on progress towards completion.

Once make test-unit-proto succeeds, we will have a separate PR that flips the switch and makes this the default test configuration.

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[tac0turtle]

LGTM