chore(ci): update Go to 1.27.1

[taigrr]

Summary

• update go.mod to Go 1.27.1
• align CI test matrix, lint, govulncheck, and Codecov upload target with Go 1.27.1
• guard command execution when the cached systemctl binary path no longer starts a process
• add regression coverage for the missing-binary execution path

Validation

• go generate ./...
• go build ./...
• go vet ./...
• staticcheck ./...
• go test -race ./...
• goimports -w .
• git diff --check