Fix go GBK load test

[Abacn]

After recent Flink runner improvments and test infra fixes (#39191 #39154), we can revert the decreasing load in (#34071 #33898)

Part of #33753

Tested:

https://github.com/apache/beam/actions/runs/31736590250

https://github.com/apache/beam/actions/runs/31814279494/job/94812092746 (10b and 100b test still failing, reverted after test run)

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[Abacn]

R: @Amar3tto @aIbrahiim

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[aIbrahiim]

LGTM