Fixed : Twenty Twelve Theme Sub Menu Z-Index Issue

[narenin]

Trac ticket: https://core.trac.wordpress.org/ticket/55892

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[github-actions]

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Props narenin, karmatosed.

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[github-actions]

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[karmatosed]

@narenin there is a recommendation on the track ticket to move this PR to use 99999 index, could you iterate?

[narenin]

@karmatosed Sure will do that.

[karmatosed]

Thank you @narenin.

[narenin]

@karmatosed I have done the same, could you please take a look.