Correctly identify whether the server supports `utf8mb4_520`

[dd32]

In older versions of PHP $db_version will be 5.5.5 for MariaDB, which prevents the use of the utf8mb4_unicode_520_ci collation.

See https://core.trac.wordpress.org/changeset/54384

This merges https://github.com/WordPress/wordpress-develop/commit/fed98bd9ef9a232d102c41e74944d3c21cd6183e & https://github.com/WordPress/wordpress-develop/commit/11df92738b07de35ae42fa6ee14c5ed506432241 to HyperDB.

[dd32]

See https://github.com/WordPress/wordcamp.org/issues/1310

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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