Fix parameters order in the implode for PHP 7.4 compatibility

[NightHunterSV]

On one of the clients' projects we've noticed an error message about the deprecation of the order of the parameters used:

The site is currently on PHP 7.4, and there was deprecated the reverse order of parameters: https://www.php.net/manual/en/migration74.deprecated.php

Make sure these boxes are checked before asking for review of your pull request - thank you!

Steps for review

• Run the build on PHP 7.4.
• Go to some theme settings page.
• Verify there are no error messages regarding the wrong parameters order on the implode call.

General checks

• All coding styles are fulfilled and there are no any issues reported by CodeSniffer. See Code of Conduct.
• Try to use Conventional commit messages accordingly to the standard https://www.conventionalcommits.org/en/v1.0.0/#specification
• Documentation has been updated according to PR changes.
• Steps for review have been provided according to PR changes.
  
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Thank you for your contribution!

[gundevel]

Can one of the admins verify this patch? Use "o+k to test" or ''t+est this please" for manual build execution.

[podarok]

@shelleygoetz @sarah-halby to include this into next point release, please

Thank you @NightHunterSV

[gundevel]

Can one of the admins verify this patch? Use "o+k to test" or ''t+est this please" for manual build execution.

[sarah-halby]

@podarok to clarify, the next release on Nov 9 or the next point release in December?

[gundevel]

Can one of the admins verify this patch? Use "o+k to test" or ''t+est this please" for manual build execution.

[podarok]

@sarah-halby for next "any" release

[gundevel]

Can one of the admins verify this patch? Use "o+k to test" or ''t+est this please" for manual build execution.

[shelleygoetz]

Added to Jira: https://openy.atlassian.net/browse/MAINTAIN-181

[gundevel]

Can one of the admins verify this patch? Use "o+k to test" or ''t+est this please" for manual build execution.