fix(ci): add safe.directory config to fix git fetch in container (#6064)

The "Fetch base branch" step fails with exit code 128 when running
inside the golang:latest container because Git does not recognize the
workspace as a safe directory. This is a Git security feature (CVE-2022-24765)
that blocks operations in directories owned by a different user, which
happens when actions/checkout runs inside a container.

https://claude.ai/code/session_01NBtQtSPnsSvAwqUMBMLGFh

Co-authored-by: Claude <[email protected]>