ci: add stable Node test matrix gate

[jbeckwith-oai]

Summary

• add a stable test matrix check that depends on every Node.js matrix variant
• fail the summary unless the complete matrix succeeds
• give the intentionally skipped internal-PR instance a distinct name so it cannot satisfy branch protection

This lets the main ruleset replace version-specific checks such as test (20) and test (26.2.0) with one stable context after this change lands.

Validation

• git diff --check
• YAML syntax parse
• actionlint v1.7.12

Rollout

Keep the current version-specific required checks until this PR merges and test matrix has run successfully on the default workflow. Then replace the four Node-version contexts in the ruleset with test matrix.

[openai-sdks]

OkTest Summary

✅ 237/237 SDK tests passed in 8.522s for Node SDK PR #2013.

Test results — 42 files

Test	Result	Time
tests/chat-completions-complex-body.test.ts	✅ Passed	121ms
tests/chat-completions-create.test.ts	✅ Passed	165ms
tests/chat-completions-stream.test.ts	✅ Passed	128ms
tests/files-content-binary.test.ts	✅ Passed	111ms
tests/files-create-multipart.test.ts	✅ Passed	130ms
tests/files-list-pagination.test.ts	✅ Passed	123ms
tests/initialize-config.test.ts	✅ Passed	185ms
tests/instance-isolation.test.ts	✅ Passed	76ms
tests/models-list.test.ts	✅ Passed	116ms
tests/responses-background-lifecycle.test.ts	✅ Passed	142ms
tests/responses-body-method-errors.test.ts	✅ Passed	267ms
tests/responses-cancel-timeout.test.ts	✅ Passed	172ms
tests/responses-cancel.test.ts	✅ Passed	168ms
tests/responses-compact-retries.test.ts	✅ Passed	215ms
tests/responses-compact.test.ts	✅ Passed	158ms
tests/responses-create-advanced-stream.test.ts	✅ Passed	98ms
tests/responses-create-advanced.test.ts	✅ Passed	151ms
tests/responses-create-disconnect.test.ts	✅ Passed	1.012s
tests/responses-create-errors.test.ts	✅ Passed	159ms
tests/responses-create-malformed-api-responses.test.ts	✅ Passed	110ms
tests/responses-create-retries.test.ts	✅ Passed	167ms
tests/responses-create-stream-failures.test.ts	✅ Passed	149ms
tests/responses-create-stream-timeout.test.ts	✅ Passed	2.129s
tests/responses-create-stream-wire.test.ts	✅ Passed	1.956s
tests/responses-create-stream.test.ts	✅ Passed	65ms
tests/responses-create-terminal-states.test.ts	✅ Passed	222ms
tests/responses-create-timeout.test.ts	✅ Passed	183ms
tests/responses-create.test.ts	✅ Passed	115ms
tests/responses-delete.test.ts	✅ Passed	95ms
tests/responses-input-items-errors.test.ts	✅ Passed	132ms
tests/responses-input-items-list.test.ts	✅ Passed	136ms
tests/responses-input-items-options.test.ts	✅ Passed	79ms
tests/responses-input-tokens-count-timeout.test.ts	✅ Passed	190ms
tests/responses-input-tokens-count.test.ts	✅ Passed	161ms
tests/responses-malformed-inputs.test.ts	✅ Passed	1.627s
tests/responses-not-found-errors.test.ts	✅ Passed	193ms
tests/responses-parse.test.ts	✅ Passed	172ms
tests/responses-retrieve-retries.test.ts	✅ Passed	245ms
tests/responses-retrieve.test.ts	✅ Passed	181ms
tests/responses-stored-method-errors.test.ts	✅ Passed	492ms
tests/retry-behavior.test.ts	✅ Passed	2.932s
tests/sdk-error-shape.test.ts	✅ Passed	193ms

View OkTest run #30113017730

_{SDK merge (e7cdbc8eeb51) · head (7bc2e5890eec) · base (04671d278ef1) · OkTest (91635c6a2723)}

[HAYDEN-OAI]

Reviewed the stable Node.js matrix gate against the live push and pull-request runs. All four Node versions complete before the test matrix gate, and the skipped internal-PR job cannot satisfy the required check. No blocking findings. Non-blocking: GitHub displays the skipped job naming expression literally. After merging, replace the four version-specific required checks with test matrix while retaining the GitHub Actions integration.