Update makeseeds.py for 0.26.x

Summary: Filter the seeds for nodes that use version 0.26.x or 0.25.x.

Test Plan: There is no easy way to test without a complete seeder setup, but this is trivial and the result visible upon next automated seed update.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11904