External Libraries: Update random_compat to version 2.0.21.
The latest release includes improved compatibility with PHP 8.1, as well as some bug fixes for Windows platforms.
Release notes:
https://github.com/paragonie/random_compat/releases/tag/v2.0.21
For a full list of changes in this update, see the random_compat GitHub:
https://github.com/paragonie/random_compat/compare/v2.0.11...v2.0.21
Follow-up to [42130].
Props jrf, paragoninitiativeenterprises.
Fixes #55181.
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