[BUGFIX] Wrong path reference for installToolPassword option

The [BE][installToolPassword] contains a suggestion to additionally
protect the Install Tool by protecting its folder by some server means.
The path specified is the legacy path /typo3/install/ which is only
a redirect to typo3/sysext/install/Start/, so the protection should
be on that folder.

Resolves: #58720
Releases: 6.2
Change-Id: I593b54878d0be7bd0307a6a5625173e6bbc58fa0
Reviewed-on: https://review.typo3.org/30027
Reviewed-by: Christian Ludwig
Tested-by: Christian Ludwig
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn