Help: Fix indentation level in fileapi docs for target attribute 'launchers'

The cmake documentation from the master branch currently contains:

install

    Optional element that is present if the target has an install() rule. The value is a JSON object with members:
    ... 

    launchers

This indicates that the attribute "launchers" would be under the attribute "install", which is not correct and is fixed with this merge request.

This was missed in !8964 (merged).

Issue: #25408 (closed)
Topic-rename: doc-fileapi-launchers