Flaky test TestOnlineDDLVDiff: add additional check for vreplication workflow to exist

[rohit-nayak-ps]

Description

We were checking for the Online DDL to reach OnlineDDLStatusRunning before checking for the status of the underlying VReplication workflow. However in executor.ExecuteWithVReplication() OnlineDDLStatusRunning is set before the VReplication records are created, resulting in flakiness in subsequent checks where we wait for the workflow to reach Running status.

This PR adds another wait for the VReplication Workflow to be created.

Related Issue(s)

• Vdiff Support for Online DDL Workflows #12965
• VDiff/OnlineDDL: add support for running VDiffs for OnlineDDL migrations #15546

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.40%. Comparing base (0912690) to head (231c812).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15695   +/-   ##
=======================================
  Coverage   68.40%   68.40%           
=======================================
  Files        1556     1556           
  Lines      195121   195121           
=======================================
+ Hits       133468   133474    +6     
+ Misses      61653    61647    -6     

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[mattlord]

❤️

[shlomi-noach]

Followup to #15546