Add an erronously missing check for error on ctx.MkdirAll(...)
Add an erronously missing check for error on ctx.MkdirAll(...)

PiperOrigin-RevId: 432245155
Change-Id: I1fe9f7feaf592d2e90479ca8ec39095cdbfe4529

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks