[Documentation] Squiz: normalise indentation of closing CDATA tags

[jaymcp]

Description

This PR updates the documentation for the Squiz standard, correcting the indentation of the closing CDATA tags.

Suggested changelog entry

Normalise indentation of CDATA tags in documentation for Squiz standard

Related issues/external references

Per discussion in #352 (comment)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
  • This change is only breaking for integrators, not for external standards or end-users.
• Documentation improvement

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the Contribution Guidelines.
• I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• I have added tests to cover my changes.
• I have verified that the code complies with the projects coding standards.
• [Required for new sniffs] I have added XML documentation for the sniff.

[jrfnl]

@jonmcp Thanks for doing this! It really helps to make things more consistent.