chore: Update CODEOWNERS to use coding-workflows sub-teams

[vaind]

Summary

• Replace @getsentry/coding-workflows with @getsentry/coding-workflows-sentry-backend and @getsentry/coding-workflows-sentry-frontend sub-teams in CODEOWNERS
• Backend paths (/src/sentry/prevent/, /src/sentry/seer/code_review/, etc.) → coding-workflows-sentry-backend
• Frontend paths (/static/app/components/prevent/, /static/app/views/prevent/, etc.) → coding-workflows-sentry-frontend

Follows getsentry/security-as-code#2538 which renames and nests these teams under the coding-workflows parent.

Test plan

• Verified no other CODEOWNERS references to the old parent team remain

[github-actions]

Backend Test Failures

Failures on efcb35e in this run:

tests/sentry/api/test_api_owners.py::APIOwnersTestCase::test_api_owner_is_a_valid_code_owner — log

tests/sentry/api/test_api_owners.py:22: in test_api_owner_is_a_valid_code_owner
    assert owner.value in self.teams
E   AssertionError: assert 'coding-workflows' in {'alerts-create-issues', 'alerts-notifications', 'codecov', 'coding-workflows-sentry-backend', 'crons', 'dashboards', ...}
E    +  where 'coding-workflows' = <ApiOwner.CODING_WORKFLOWS: 'coding-workflows'>.value
E    +  and   {'alerts-create-issues', 'alerts-notifications', 'codecov', 'coding-workflows-sentry-backend', 'crons', 'dashboards', ...} = <tests.sentry.api.test_api_owners.APIOwnersTestCase testMethod=test_api_owner_is_a_valid_code_owner>.teams

[github-actions]

Backend Test Failures

Failures on 5f50d43 in this run:

tests/sentry/api/test_api_owners.py::APIOwnersTestCase::test_api_owner_is_a_valid_code_owner — log

tests/sentry/api/test_api_owners.py:22: in test_api_owner_is_a_valid_code_owner
    assert owner.value in self.teams
E   AssertionError: assert 'coding-workflows' in {'alerts-create-issues', 'alerts-notifications', 'codecov', 'coding-workflows-sentry-backend', 'crons', 'dashboards', ...}
E    +  where 'coding-workflows' = <ApiOwner.CODING_WORKFLOWS: 'coding-workflows'>.value
E    +  and   {'alerts-create-issues', 'alerts-notifications', 'codecov', 'coding-workflows-sentry-backend', 'crons', 'dashboards', ...} = <tests.sentry.api.test_api_owners.APIOwnersTestCase testMethod=test_api_owner_is_a_valid_code_owner>.teams