Bump version to 0.16.2-gitlab.53

Summary

Bump docker-machine to 0.16.2-gitlab.53 for the next stable release.

The release includes the opt-in Google flex-selection stockout cooldown from !188 (merged). The cooldown defaults to disabled, so publishing this release does not change selection behavior until a runner-manager cohort explicitly enables it.

Release steps after merge

1. Create the signed tag:

   git tag -s v0.16.2-gitlab.53 -m "Version 0.16.2-gitlab.53"
   git push origin v0.16.2-gitlab.53

2. Confirm the tag pipeline's release stable S3 job publishes the binaries under v0.16.2-gitlab.53.
3. Verify the Linux artifact checksum and reported version from the immutable tag-specific S3 path.
4. Canary the new binary with the cooldown disabled before enabling it on a bounded runner-manager cohort.

Related:

• !188 (merged)
• https://gitlab.com/gitlab-com/gl-infra/production-engineering/-/work_items/29633 (confidential)

Validation

• go test ./version
• make build
• !188 (merged) merge-train pipeline passed.
• Full local make validate reaches the existing drivers/vmwarefusion vet findings unrelated to this version-only change; the MR pipeline is the canonical validation environment.