Log Message:
Update to 8.6.12

Upstream changes:
8.6.12
The third-party Twig library, which powers Drupal 8's theme system, recently \ 
released new versions (Twig 1.38.0 and 1.38.1) that introduced a fatal error for \ 
Drupal 8 sites using Composer. Drupal 8.6.11 was released yesterday with an \ 
update to Twig 1.38.2 in order to resolve that error. However, this update also \ 
led to a different regression for certain Drupal 8 themes that use Twig {% embed \ 
%} tags. This release hotfixes Drupal 8 to resolve that regression. No other \ 
changes are included.

8.6.11
This release resolves two critical issues affecting Drupal 8 site updates:

    The third-party Twig library, which powers Drupal 8's theme system, recently \ 
released a new minor version (1.38.0) that introduced a fatal error when used \ 
with Drupal 8. As a result, Drupal 8 sites managed with Composer encountered \ 
this fatal error when updating Twig to version 1.38.0 or 1.38.1. This release \ 
updates Drupal to require Twig 1.38.2, which resolves the fatal error.

    The recent releases for SA-CORE-2019-003 introduced a serialized data \ 
integrity issue affecting some contributed and custom modules, including the \ 
Default Content and Paragraphs modules. This release resolves the issue for \ 
affected sites.

Additionally, this release resolves an administrator-only access bypass with the \ 
Layout Builder module. Previously, users who didn't have access to view \ 
individual entities were still granted access to configure the layout for that \ 
entity (if per-entity layout configuration was enabled) and therefore could view \ 
its content. This implicit access has been removed. Site owners should ensure \ 
that all content editor roles have access to view the content for which they are \ 
configuring the layout.