updates buildkit to 0.18.2 and fixes building locally

[jaxesn]

Issue #, if available:

Description of changes:

Bumps to the latest buildkit. I tested this on the eks-anywhere prow jobs using the old buildkit-rootless sidecar to confirm the buildctl client works with the older sidecar. We are going to update the sidecar container version on eks-a, eks-d does not have to update theirs immediately.

While building locally ran into an issue with the golang checksums path being hardcoded to prow. Fixed this.

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