chore(ci): avoid duplicate LoongSuite push runs

[sipercai]

Description

Limit generated LoongSuite CI workflows so push runs only for main, while keeping pull_request and merge_group triggers.

This avoids running a duplicate full LoongSuite matrix when a same-repository PR branch receives a new commit. PR updates remain covered by the pull_request trigger.

This also changes LoongSuite lint/test workflows from static per-package jobs with job-level skips to detector-driven dynamic matrices:

• loongsuite_changes computes full, packages, degraded, and a dynamic matrix.
• Package-scoped PRs create only the selected package's lint/test matrix entries.
• No-package LoongSuite changes skip the matrix job and pass through an aggregate result job.
• Release/backport, merge queue, main push, shared CI files, unknown packages, and degraded detector paths still run the full LoongSuite matrix.
• The generated lint/test workflows now expose stable aggregate result jobs instead of hundreds of skipped per-package checks.

Fixes # (none)

Branch Protection Note

This PR intentionally changes the LoongSuite lint/test check shape.

Before merging, branch protection / merge queue required checks should be updated from old per-package LoongSuite lint/test checks, for example:

• LoongSuite loongsuite-instrumentation-google-adk
• LoongSuite loongsuite-instrumentation-google-adk-oldest 3.10 Ubuntu
• other per-package LoongSuite ... lint/test matrix checks

to the new aggregate checks:

• LoongSuite Lint 0 result
• LoongSuite Test 0 result

The existing LoongSuite misc checks can remain separate.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• tox -e generate-workflows
• tox -c tox-loongsuite.ini -e py311-test-detect-loongsuite-changes
• tox -e precommit
• git diff --check
• python $PIPELINE_SKILL_DIR/scripts/check_loongsuite_pr_readiness.py --repo .
• Generated LoongSuite workflow YAML parses successfully
• Matrix selection smoke check:
  • loongsuite-instrumentation-google-adk: 1 lint job, 10 test jobs
  • loongsuite-instrumentation-crewai: 1 lint job, 4 test jobs
  • loongsuite-instrumentation-litellm: 1 lint job, 4 test jobs
  • full run: 12 lint jobs, 98 test jobs
  • no package changes: 0 lint jobs, 0 test jobs
• Codex-Claude team review completed with no remaining code blockers

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

Changelog and documentation updates are not included because this is a CI-only workflow change.