Restore original return value for WP_Script_Modules::get_dependencies()

[westonruter]

See https://core.trac.wordpress.org/ticket/61734#comment:55

This reverts the WP_Script_Modules::get_dependencies() change in 25420f0 which was developed in #9867 to fix Core-63486.

As of WP 6.8, WP_Script_Modules::get_dependencies() had this return signature:

wordpress-develop/src/wp-includes/class-wp-script-modules.php

Line 306 in 58edb2f

* @return array[] List of dependencies, keyed by script module identifier.

The aforementioned commit for 6.9 changed it to:

wordpress-develop/src/wp-includes/class-wp-script-modules.php

Line 569 in 7a840d3

* @return string[] List of IDs for script module dependencies.

Since the method was private, I didn't think there would be a problem to make this change. However, it turns out that Query Monitor is using this private method via the Reflection API. This is because core is not yet exposing the necessary accessor methods from WP_Script_Modules, and so QM is forced to use a private method. This is something which should be no longer be necessary as of Core-60597.

In the meantime, we can restore the original return value for the method since it isn't particularly difficult to do so for 6.9-beta2.

Trac ticket: https://core.trac.wordpress.org/ticket/61734

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[pbiron]

An initial test of this PR applied to 6.9-beta1 seems to resolve the problem I reported in https://core.trac.wordpress.org/ticket/61734#comment:52. I'll test some more tomorrow.