Fix failing unit test by missing svg

[ScottVerbeek]

This will add the disabled icon to the pix library of the module, resolving the previously failing unit test

$ vendor/bin/phpunit --filter="test_svg_fallback"
Moodle 4.3.4+ (Build: 20240530), 11a2641a137bf21552868a24d6439011e027ebe3
Php: 8.1.28, pgsql: 16.0 (Debian 16.0-1.pgdg120+1), OS: Linux 6.4.12-060412-generic x86_64
PHPUnit 9.5.28 by Sebastian Bergmann and contributors.

.                                                                   1 / 1 (100%)

Time: 00:05.430, Memory: 342.00 MB

OK (1 test, 508 assertions)

The output of failing unit test before this change

Moodle 4.3.4+ (Build: 20240530), 11a2641a137bf21552868a24d6439011e027ebe3
Php: 8.1.28, pgsql: 16.0 (Debian 16.0-1.pgdg120+1), OS: Linux 6.4.12-060412-generic x86_64
PHPUnit 9.5.28 by Sebastian Bergmann and contributors.

F                                                                   1 / 1 (100%)

Time: 00:05.554, Memory: 340.00 MB

There was 1 failure:

1) core\output\icon_system_fontawesome_test::test_svg_fallback
No SVG equivalent found for 'tool_lifecycle:t/disable'
Failed asserting that false is true.

/var/www/moodle-43/lib/tests/output/icon_system_fontawesome_test.php:56
/var/www/moodle-43/lib/phpunit/classes/advanced_testcase.php:81

FAILURES!
Tests: 1, Assertions: 495, Failures: 1.

[justusdieckmann]

Thank you very much!