Review CI workflow for Otto - optimize dependency handling

[austinlparker]

Review and optimize the GitHub Actions CI workflow for Otto:

1. Evaluate whether the explicit dependency download step is necessary
2. The current workflow has followed by ? github.com/open-telemetry/sig-project-infra/otto/cmd/otto [no test files]
   === RUN TestIsSlashCommand
   --- PASS: TestIsSlashCommand (0.00s)
   === RUN TestRegisterModuleAndDispatch
   2025/04/21 12:36:22 INFO module registered name=testmod
   --- PASS: TestRegisterModuleAndDispatch (0.00s)
   PASS
   ok github.com/open-telemetry/sig-project-infra/otto/internal 0.389s
   2025/04/21 12:36:22 INFO module registered name=oncall
   === RUN TestAddTaskAndGetTaskByIssueNumber
   --- PASS: TestAddTaskAndGetTaskByIssueNumber (0.00s)
   === RUN TestTaskAcknowledge
   --- PASS: TestTaskAcknowledge (0.00s)
   PASS
   ok github.com/open-telemetry/sig-project-infra/otto/modules 0.580s which may be redundant
3. Optimize CI speed while maintaining reliability

Based on feedback from PR #3: #3 (comment)