Are you talking about just the OpenMapTiles spec, or some adjacent software? I'm certain that you can build software to some specification without ever agreeing to the spec text's licence, and that a CC-BY licenced spec doesn't limit any implementing system's licence.
Even so, CC-BY is permissive and you could include CC-BY content in a, say, GPL project. You just need to include both licences.
Even so, CC-BY is permissive and you could include CC-BY content in a, say, GPL project. You just need to include both licences.