Fix docstring for batch_size in client.map

[dchudz]

closes #7382

[GPUtester]

Can one of the admins verify this patch?

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[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

       26 files  +         6         26 suites  +6   15h 42m 9s ⏱️ + 4h 22m 10s
  3 581 tests ±         0    3 469 ✔️ +         7     105 💤  -   10  7 ❌ +3 
45 340 runs  +13 024  43 167 ✔️ +12 312  2 164 💤 +707  9 ❌ +5 

For more details on these failures, see this check.

Results for commit 2e4743c. ± Comparison against base commit f4f4718.

[fjetter]

I would've preferred if the implementation actually did what the doc string said but that's unfortunately not true :(

Thanks for the fix