docs(Migration guide): fix sapUiSmallMarginBeginEnd to sapUiSmallMarginTopBottom in docs

[mrCherry97]

Thank you for your contribution! 👏

To get it merged faster, kindly review the checklist below:

Pull Request Checklist

• [x] Reviewed the Contributing Guidelines
  • Especially the How to Contribute section
• [x] Correct commit message style

[coveralls]

Pull Request Test Coverage Report for Build 11663952298

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 87.151%

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Totals
Change from base Build 11660929411:	0.02%
Covered Lines:	5053
Relevant Lines:	5798

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💛 - Coveralls