Important: #96218 - Use proper surrounding "html" tags for Fluid SystemEmail

See forge#96218

Description

Due to usage of data-namespace-typo3-fluid="true" in the <html> declaration of the file EXT:core/Resources/Private/Layouts/SystemEmail.html, the whole <html>..</html> structure is removed from a sent HTML mail.

Validation and possibly utilities like SpamAssassin may fail or negatively score these mails due to these tags being missing.

Since the xmlns declaration of the ViewHelpers is semantically not wrong, it can actually be included in the email by removing the data-namespace-typo3-fluid attribute, instead of requiring the alternate more intrusive Fluid ViewHelper declaration.

Affected installations

All setups with customizations of the file EXT:core/Resources/Private/Layouts/SystemEmail.html for sending FluidEmails.

Migration

Adjust custom copies of the file EXT:core/Resources/Private/Layouts/SystemEmail.html like this:

Before (EXT:your_extension/Resources/Private/Layouts/SystemEmail.html) 
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:v="urn:schemas-microsoft-com:vml"
      xmlns:o="urn:schemas-microsoft-com:office:office"
      xmlns:f="http://typo3.org/ns/TYPO3/CMS/Fluid/ViewHelpers"
      xmlns:core="http://typo3.org/ns/TYPO3/CMS/Core/ViewHelpers"
      data-namespace-typo3-fluid="true">
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into this:

After (EXT:your_extension/Resources/Private/Layouts/SystemEmail.html) 
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:v="urn:schemas-microsoft-com:vml"
      xmlns:o="urn:schemas-microsoft-com:office:office"
      xmlns:f="http://typo3.org/ns/TYPO3/CMS/Fluid/ViewHelpers"
      xmlns:core="http://typo3.org/ns/TYPO3/CMS/Core/ViewHelpers">
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