Add error handling to GithubProviderClient.listVersions

[Copilot]

Addresses feedback on #103 regarding unused status variable in GithubProviderClient.listVersions. The variable was initially removed, but code review revealed missing error handling compared to other provider clients.

Changes

• Added HTTP status validation with ensureOk() to listVersions method
• Aligns error handling with GitlabProviderClient and BitbucketProviderClient implementations

const { status, json } = await this.request<GithubCommit[]>(
  config,
  `/repos/${encodeURIComponent(owner)}/${encodeURIComponent(repo)}/commits?${qs.toString()}`,
);

this.ensureOk(status, "Failed to list query versions.");

Without this check, API errors would silently return empty version lists instead of throwing meaningful errors to the caller.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.