Overriding default PHP timezone with `date_default_timezone_set()`, while not recommended, should not inadvertently result in changing existing permalinks.
Add a unit test.
Props Rarst, steevithak, archon810, maciejmackowiak, Ov3rfly, Cybr, hometowntrailers, scvleon, miette49.
Merges [46795] to the 5.3 branch.
Fixes#48623.
git-svn-id: https://develop.svn.wordpress.org/branches/5.3@46796 602fd350-edb4-49c9-b593-d223f7449a82
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