[TASK] Adjust rst validation

The rst validation is adjusted to allow
one to two whitespaces between the ".."
and the "import" / "index" keywords to
support existing files as well as newly
generated (rst helper tool) ones.

Resolves: #105176
Releases: main, 12.4, 11.5
Change-Id: I566b49990e894ea19692011fe6027591df289ad7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86395


Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>