arrow

ARROW-6513: [CI] Rename conda requirements files to have txt extension instead of yml

Missing renames from #10572

Closes #10656 from kszucs/conda-txt

Authored-by: Krisztián Szűcs <szucs.krisztian@gmail.com>
Signed-off-by: Krisztián Szűcs <szucs.krisztian@gmail.com>