`task` Fix id-generation

[dacbd]

:hear_no_evil: Much sad! 8 hrs of debugging for such a small fix :see_no_evil:

my day's TLDR:

Any id/name greater than 28 aka: maximumLongLength-shortLength-uint32(len("tpi---")) resulted in improperly generating the digest and so the inferred bucket name was different from terraform create to terraform refresh which results in the follow error:

Discovered via some BB testing because below Bitbucket CI env is a uuid and thus >28 you can also replicate the error by setting a name for your task that is also >28 chars: https://github.com/iterative/terraform-provider-iterative/blob/c3f1c08c60d32b954e8e23b23feae2e7431100c5/iterative/resource_task.go#L371-L388