Update GetID3 to version 1.9.21

[jrf]

GetID3 1.9.21 has just been released and includes preliminary PHP 8.1 support, as well as a variety of bugfixes.

The version included with WP should be updated.

Full details:

• ​https://github.com/JamesHeinrich/getID3/releases/tag/v1.9.21
• ​https://github.com/JamesHeinrich/getID3/compare/v1.9.20...v1.9.21

I've NOT reviewed the diff yet, but would strongly recommend an update at the earliest convenience due to the PHP 8.1 fixes being included.

Previously: [47601], [48278]
Related: #53635

[SergeyBiryukov]

In 51900:

External Libraries: Update getID3 to version 1.9.21.

The latest version includes preliminary PHP 8.1 support, as well as a variety of bug fixes.

Release notes: ​https://github.com/JamesHeinrich/getID3/releases/tag/v1.9.21

A full list of changes in this update can be found on GitHub:
​https://github.com/JamesHeinrich/getID3/compare/v1.9.20...v1.9.21

This commit also includes PHPCS adjustments previously made for a passing PHP Compatibility scan.

Follow-up to [47601], [47737], [47902], [48278], [49621], [50714].

Props jrf, SergeyBiryukov.
Fixes #54162.

[SergeyBiryukov]

Looks like [51900] caused ​unit test failures:

There were 3 errors:

1) Tests_Media::test_wp_read_audio_metadata_adds_creation_date_with_mp4
Undefined index: created_timestamp

/var/www/tests/phpunit/tests/media.php:2557

2) Tests_Media::test_wp_read_video_metadata_adds_creation_date_with_quicktime
Undefined index: created_timestamp

/var/www/tests/phpunit/tests/media.php:2567

3) Tests_Media::test_wp_read_video_metadata_adds_creation_date_with_mp4
Undefined index: created_timestamp

/var/www/tests/phpunit/tests/media.php:2577

[SergeyBiryukov]

In 51901:

External Libraries: Revert [51900] for now to investigate test failures.

See #54162.

[SergeyBiryukov]

#54285 was marked as a duplicate.