fix: add table cell style vMerge="continue"

[raybon-lee]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Fixes # (issue)

Checklist:

• [ Y] I have run composer run-script check --timeout=0 and no errors were reported

Checked all files in 0.117 seconds, 14.000 MB memory used
phpcs --report-width=200 --report-summary --report-full samples/ src/ tests/ --ignore=src/PhpWord/Shared/PCLZip --standard=PSR2 -n
phpmd src/,tests/ text ./phpmd.xml.dist --exclude pclzip.lib.php
/Users/raybon/Sites/PHPWord/src/PhpWord/Element/TOC.php:27 CamelCasePropertyName The property $TOCStyle is not named in camelCase.
Script phpmd src/,tests/ text ./phpmd.xml.dist --exclude pclzip.lib.php handling the check event returned with error code 2

• [ N] The new code is covered by unit tests (check build/coverage for coverage report)
• [ N] I have updated the documentation to describe the changes

[github-actions]

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