use a fresh per-job checkout directory for test, standards, and
thirdparty update workflows instead of reusing a shared repo path.
align the Gitea standards-check template with the same isolation
strategy and expand workflow bootstrap regression coverage.
remove the pre-checkout dependency on .gitea/ci/prepare_repo.sh
from the root workflows and inline the bootstrap logic instead.
add a regression test for workflow bootstrap ordering and register
it in the tests README.
Replace duplicated inline checkout logic in standards-check.yml and
test.yml with a call to .gitea/ci/prepare_repo.sh. Also remove the
unused TEST_WORKSPACE env var from test.yml.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>