Wire api/incubator test suites into check

[thswlsqls]

Fixes #8690

Description

• api/incubator/build.gradle.kts registers the testConvertToModel JvmTestSuite but never wires it into check, so its 4 tests have not run in CI since Add new convenience methods for converting DeclarativeConfigProperties to config model #7453 added the suite (2025-07-10).
• The sources still compile and pass checkstyle, so nothing looks broken.
• Adds the tasks { check { dependsOn(testing.suites) } } block that sdk/trace, sdk/logs, context and seven other modules already use.
• docs/knowledge/testing-patterns.md states this rule, but it was added later, in Rework CONTRIBUTING.md, extracting bits to new /docs/knowledge/* for … #8303 (2026-06), so this module was never brought in line.
• Of the 14 modules registering a JvmTestSuite, 11 wire it. :exporters:otlp:common has the same gap; happy to follow up once this lands.

Testing done

• Build wiring only: no production code, signature or public API change, so no test was added.
• ./gradlew :api:incubator:check --dry-run now lists :api:incubator:testConvertToModel; it was absent before.
• ./gradlew :api:incubator:check — 101 tests passed (97 existing plus the 4 from the newly wired suite).
• docs/apidiffs/ is untouched.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.62%. Comparing base (dd811c4) to head (1e2b759).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8691   +/-   ##
=========================================
  Coverage     91.62%   91.62%           
  Complexity    10327    10327           
=========================================
  Files          1003     1003           
  Lines         27138    27138           
  Branches       3187     3187           
=========================================
  Hits          24866    24866           
  Misses         1566     1566           
  Partials        706      706           

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