Fix finite field GF(p).extension(1, names=tuple)

[user202729]

Fix #40926 .

there's an alternative way of calling normalize_names(1, name) (which internally calls certify_name anyway) where normalize_names accepts various name formats, but as far as I can see, that will accept any additional name format than what is accepted by 1 generator.

See also the follow-up in #40949

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