Indented code blocks don't get auto-fixed

[GuySartorelli]

Identified in #1 (comment)

If a code block is indented, e.g. as part of a list item, issues in the block will be correctly identified by the sniff but not fixed when the --fix option is passed in.

There's an example of this in the unit test fixtures - see

markdown-php-codesniffer/tests/expected-after-fixing/lint-with-problems.md

Lines 37 to 44 in 47f0c4d

	For some reason this one doesn't get auto-fixed.
	- this one will be indented
	```php
	class FinalClass {
	private string $lastProperty='this is the value';
	}
	```

Acceptance criteria

• Fixable linting issues in indented code blocks are fixed
• The note about them not being fixable is removed