move the tst test_http_response_code_constants from http.php to getStatusHeaderDesc.php

[pbearne]

Let's get all tests into the same file

Moves test_http_response_code_constants() from the HTTP API test file into the test class for get_status_header_desc(), so all tests for that function live in one place.

What the problem was:

• test_http_response_code_constants() exercises get_status_header_desc() but was located in tests/phpunit/tests/http/http.php (Tests_HTTP_HTTP).

What the fix does:

• Moves the test method into Tests_Functions_GetStatusHeaderDesc (tests/phpunit/tests/functions/getStatusHeaderDesc.php).
• Drops the redundant method-level @covers ::get_status_header_desc, as the class-level docblock already declares it.

Approach and why:

• Test body is unchanged; this only relocates it to the canonical file for the function under test, improving discoverability and grouping.

Trac ticket: https://core.trac.wordpress.org/ticket/65527

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[SergeyBiryukov]

In 62593:

Tests: Move the HTTP response codes test for consistency.

While the test was originally written to verify that the WP_Http class has all the HTTP response codes as constants, it ensures that the constants match the response codes stored in the $wp_header_to_desc global used by the get_status_header_desc() function, so the latter's unit test file appears to be the logical placement.

Follow-up to [36749], [46107].

Props pbearne, khokansardar, SergeyBiryukov.
Fixes #65527.