feat(ci): tag starter-smoke Slack alerts with their source repo

The starter smoke-test Slack alert had no indication of where it came
from, which is ambiguous when the same workflow runs across multiple
repos (e.g. the public CopilotKit/CopilotKit repo vs the internal
testybara fork). Prepend a `[ci:<owner/repo>]` tag derived from
github.repository so triage is unambiguous about the source. These CI
alerts test example source and carry no staging/production dimension,
so [ci] is the meaningful source axis. Existing message format is
otherwise preserved.

Author: jpr5

.github/workflows/test_smoke-starter.yml

@@ -167,4 +167,4 @@ jobs:
           webhook: ${{ secrets.SLACK_WEBHOOK_OSS_ALERTS }}
           webhook-type: incoming-webhook
           payload: |
-            { "text": ${{ toJSON(format(':x: *Starter smoke test failing: {0}*\n<{1}/{2}/actions/runs/{3}|View run> · <{1}/{2}/actions/runs/{3}/job/{4}|View job>\n```{5}```', matrix.starter, github.server_url, github.repository, github.run_id, github.job, env.summary)) }} }
+            { "text": ${{ toJSON(format(':x: `[ci:{2}]` *Starter smoke test failing: {0}*\n<{1}/{2}/actions/runs/{3}|View run> · <{1}/{2}/actions/runs/{3}/job/{4}|View job>\n```{5}```', matrix.starter, github.server_url, github.repository, github.run_id, github.job, env.summary)) }} }