from PR #925

The tag name length restriction was increased to 256 characters last year [1]. Because of this, MBS started using more informative tag names [2] but it turns out that the tag name is also used to create the build target. We'd like to keep the naming consistent and to do this, we must increases the length restriction on build target names.

1 - https://pagure.io/koji/c/d9280d694501afb2df6c12b3f9778beb73f350a0?branch=master
2 - https://pagure.io/fm-orchestrator/issue/918