[Documentation]: normalise indentation of CDATA tags in sniff documentation

[jaymcp]

Description

This PR normalises CDATA tag indentation in sniff documentation.
The original intention was to open separate PRs for changes to every standard, but it was primarily Squiz that was affected, which was addressed in #361. These are the last few instances of incorrect indentation that I found across all other standards.

Suggested changelog entry

Normalise indentation of CDATA tags in sniff documentation.

Related issues/external references

Per discussion #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]

Thanks @jonmcp for verifying all that and tidying it up!