ARROW-14437: [Python] Make CSV cancellation test more robust
ARROW-14437: [Python] Make CSV cancellation test more robust

Size the workload according to the machine speed, to increase the probability of actually triggering cancellation.

Closes #11598 from pitrou/ARROW-14437-csv-cancellation-test

Authored-by: Antoine Pitrou <9359a4d812173b65a3a0094cd86363e79731a3c2@python.org>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

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