Fix the broken flink tests by optimizing conf

[liferoad]

Fixes #32794. Following https://nightlies.apache.org/flink/flink-docs-master/docs/deployment/memory/mem_setup_tm/#detailed-memory-model, optimize runners/flink/src/test/resources/flink-conf.yaml and switch to this conf for the flink tests.

Tested locally for both Python 3.12 and 3.9:

./gradlew :sdks:python:test-suites:portable:py39:flinkExamples --max-workers=8 --continue \                     
   -Dorg.gradle.jvmargs=-Xms2g -Dorg.gradle.jvmargs=-Xmx6g -Dorg.gradle.vfs.watch=false -Pdocker-pull-licenses \
  -PpythonVersion=3.12

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[damccorm]

Thanks!