mounter(ticdc): timezone fill default value should also consider tz. (#10932)

[ti-chi-bot]

This is an automated cherry-pick of #10932

What problem does this PR solve?

Issue Number: close #10931

What is changed and how it works?

• Ensure to correctly set the default value for the timestamp. It's in UTC and needs to be changed to the timezone set by TiCDC.

Check List

Tests

• Unit test
• Integration test

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

`None`

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-chi-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.0@b81378b). Learn more about missing BASE report.

Additional details and impacted files

Components	Coverage Δ
cdc	61.8931% <0.0000%> (?)
dm	51.2616% <0.0000%> (?)
engine	63.3936% <0.0000%> (?)

Flag	Coverage Δ
unit	57.5654% <75.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             release-8.0     #10949   +/-   ##
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  Coverage               ?   57.5654%           
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  Files                  ?        853           
  Lines                  ?     126899           
  Branches               ?          0           
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  Hits                   ?      73050           
  Misses                 ?      48409           
  Partials               ?       5440           

[3AceShowHand]

/retest