Fix CI project include error when a project is invalid

What does this MR do and why?

This MR fixes the CI project-include error defined in #406813 (closed) which was introduced by !114279 (merged).

In this MR, we will

• return nil for can_access_local_content and sha if project is nil
• force-load the project when calculating the batch key

These changes are still behind the FF ci_batch_project_includes_context (#392746 (comment 1367065552)).

Screenshots or screen recordings

include:
  - project: root/project-a
    file: .gitlab-ci.yml
  - project: invalid/project
    file: xyz.yml

build:
  script: exit 0

Before this MR:

After this MR:

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.