NodeFormAlter.php issue when site is in Read Only Mode (not set $form['actions']) [#3487080]

Problem/Motivation

When a site is set to read only via readonlymode (https://www.drupal.org/project/readonlymode) the $form['actions'] array is unset to prevent submitting forms.

NodeFormAlter.php:187 attempts to add form validation to forms via $form['actions']. They have already been unset though by readonlymode, and so array_values() complains that:

TypeError: array_keys(): Argument #1 ($array) must be of type array, null given in array_keys() (line 190 of modules/contrib/group_content_menu/src/NodeFormAlter.php).

Steps to reproduce

-Install readonlymode and group_content menu
-Enable read only mode
-Attempt to create a node in a group, as a user without the permission "Access all forms while in Read Only Mode"
-See error

Proposed resolution

-A quick sanity check of !empty($form['actions']) resolves the issue.

Issue fork group_content_menu-3487080

Show commands

Start within a Git clone of the project using the version control instructions.

Add & fetch this issue fork’s repository

Or, if you do not have SSH keys set up on git.drupalcode.org:

Add & fetch this issue fork’s repository

3487080-but-without-wrong-commit changes, plain diff MR !43
Check out this branch for the first time

Check out existing branch, if you already have it locally