chore(deps): bump @opencode-ai/plugin in the opencode-ai group

Bumps the opencode-ai group with 1 update: @opencode-ai/plugin.


Updates `@opencode-ai/plugin` from 1.18.4 to 1.18.9

---
updated-dependencies:
- dependency-name: "@opencode-ai/plugin"
  dependency-version: 1.18.9
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: opencode-ai
...

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Author: dependabot[bot]