Don't load resource via CanCanCan in Api::ProjectsController

As I explained in the previous commit, the `load_project` before action
is where we want the project to be loaded, i.e. via `ProjectLoader` so
that it's found by a combination of `Project#identifier` and
`Project#locale`.

To make this clearer, I've changed the `load_and_authorize_resource`
before action to `authorize_resource` [1], so the CanCanCan
authorization uses the project found by the `load_project` before
action.

However, this meant that if the project was *not* found by the
`load_project` before action an exception was raised in
`Project::Update.call` resulting in a 422 Unprocessable Entity response
with the following error message:

    Error persisting changes: undefined method `components' for nil:NilClass

To fix this I'm now raising an `ActiveRecord::RecordNotFound` exception
in the `load_project` before action if no project is found. This results
in the expected 404 Not Found response.

I think there's a strong case to be made the this exception raising
behaviour should be added to `ProjectLoader#load`. However, that's a
bigger change with a lot more risk, so I'm going to leave that for now.

Note that I've retained the load resource functionality for the `create`
action, because the `load_project` before action isn't triggered for
`create` and the authorize resource functionality seems to rely on the
project built by the load resource step and I want to keep changes to a
minimum.

[1]: https://github.com/CanCanCommunity/cancancan/blob/3.4.0/docs/controller_helpers.md#authorize_resource-load_resource-load_and_authorize_resource

Author: floehopper

app/controllers/api/projects_controller.rb

@@ -7,7 +7,8 @@ class ProjectsController < ApiController
     before_action :authorize_user, only: %i[create update index destroy]
     before_action :load_project, only: %i[show update destroy show_context]
     before_action :load_projects, only: %i[index]
-    load_and_authorize_resource
+    load_resource only: :create
+    authorize_resource
     before_action :verify_lesson_belongs_to_school, only: :create
     after_action :pagination_link_header, only: %i[index]
 
@@ -73,6 +74,7 @@ def load_project
                  else
                    project_loader.load
                  end
+      raise ActiveRecord::RecordNotFound if @project.blank?
     end
 
     def load_projects