[HUDI-7656] Fix a flaky test for concurrent writes

[linliu-code]

Change Logs

Make sure the conflict happens since the update records are shared between the two writers.

Impact

Fix a flaky test.
Test locally for 40+ times; there are no failures.

Risk level (write none, low medium or high below)

None.

Documentation Update

Describe any necessary documentation update if there is any new feature, config, or user-facing change. If not, put "none".

• The config description must be updated if new configs are added or the default value of the configs are changed
• Any new feature or user-facing change requires updating the Hudi website. Please create a Jira ticket, attach the
  ticket number here and follow the instruction to make
  changes to the website.

Contributor's checklist

• Read through contributor's guide
• Change Logs and Impact were stated clearly
• Adequate tests were added if applicable
• CI passed

[hudi-bot]

CI report:

• 4e19952 Azure: SUCCESS

Bot commands

@hudi-bot supports the following commands:

• @hudi-bot run azure re-run the last Azure build

[nsivabalan]

LGTM

addressed your comments. moving ahead.