Update ConfigForm to accomodate constructor change introduced in D10.2.0

Problem/Motivation

The constructor for Drupal\Core\Form\ConfigFormBase change in D10.2.0. See change record. This module's ConfigForm form, which extends ConfigFormBase, cannot be loaded on D11.0.0+ due to a fatal error:

Error: Typed property Drupal\Core\Form\ConfigFormBase::$typedConfigManager must not be accessed before initialization in Drupal\Core\Form\ConfigFormBase->typedConfigManager() (line 70 of core/lib/Drupal/Core/Form/ConfigFormBase.php).

Steps to reproduce

• Load path /admin/config/development/http-status-code-test on D10.2.0 and note deprecation notice.
• Load same path on D11.0.0 and note fatal error.

Proposed resolution

Update constructor for Drupal\http_status_code_test\Form\ConfigForm.

Note: Module already requires D10.2.0+, so no need for BC code.

Remaining tasks

• File MR
• Passing tests

User interface changes

None

API changes

None

Data model changes

None