ci: restore environment secrets for race-UT summary

[aunjgr]

What type of PR is this?

• BUG
• Test and CI

Related issue / failure

MatrixOne PR matrixorigin/matrixone#28873, run 34921480932.

All four race-UT shards passed, but GitHub rejected the summary before any step ran because the required EE_DB_* secrets were unavailable. The shard jobs select the ci environment; the summary did not.

What this PR does / why we need it

Attach the race-UT summary job to the existing ci environment so required environment-scoped secrets are available during reusable-workflow job initialization. Preserve the summary's all-shards-must-succeed check and add regression coverage for environment selection, shard dependency/admission, and failure propagation.

Validation

• The new contract test fails on the original workflow because the summary lacks its environment.
• Four new unittest methods pass, including success/failure/cancelled/skipped/empty-result controls that execute the actual summary shell check.
• Existing TKE subject and coverage-artifact selection suites pass (14 tests).
• All workflow YAML parses; repository-pinned actionlint 1.7.12 passes with the existing configuration.
• git diff --check passes.

Rollout

The summary gains access to the same ci environment as the shard jobs. No secrets are copied, printed, or made optional. Test selection, timeouts, race flags, coverage, required-check name, and caller interface remain unchanged.

After merge, rerun all jobs of the current MatrixOne #28873 workflow run (not failed jobs only), verify the resolved reusable-workflow revision includes this fix, and confirm the summary starts and requires every shard to succeed. Local tests do not establish live secret availability. No MatrixOne source changes are included.