issue #557: Add SVG and PNG icon for calendar

[ScottVerbeek]

Resolves issue #557 fixing unit test test_svg_fallback on Moodle 4.3.

root@c3e2c38a9c70:/var/www/vanilla-403# vendor/bin/phpunit --filter test_svg_fallback 
Moodle 4.3.2 (Build: 20231222), 6a6043c47b80ea6f64f69d8a41487ded3444a970
Php: 8.1.24, pgsql: 14.0 (Debian 14.0-1.pgdg110+1), OS: Linux 6.4.12-060412-generic x86_64
PHPUnit 9.5.28 by Sebastian Bergmann and contributors.

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Time: 00:11.212, Memory: 344.00 MB

OK (507 tests, 507 assertions)

Fixes #557

[jrchamp]

Thanks @ScottVerbeek! We'll do some testing on our side and plan to merge this in the next release.

[jrchamp]

Hi @ScottVerbeek, I wasn't able to push directly to your branch, so I opened catalyst#1 to optimize the SVG files. With that change added on, I'd be happy to approve and merge this tomorrow.

[smbader]

Great catch, thank you for the PR.

[smbader]

@jrchamp will add SVGOMG optimizations in a separate pull request.