Fix flaky timezone test fixture (GH-18624)

[hakre]

As documented in RunningTests, tests have to be written to be independent of any php.ini file.

Without specifying the timezone, the var_dump() will make use of the default timezone that may not be the expected "UTC" timezone.

This renders the test-cases flaky and will make them fail if the date.timezone is different from the string "UTC".

Fix is to interpolate the timezone in the test fixture or to set date.timezone to UTC.

fix-up-of: GH-18624

[hakre]

@derickr This is the ext/date part from #20035, rebased. You had approved this previously – could you take another look? Thanks.

[iluuu1994]

I see there's this:

php-src/run-tests.php

Lines 187 to 190 in d34c09f

	// If timezone is not set, use UTC.
	if (ini_get('date.timezone') == '') {
	date_default_timezone_set('UTC');
	}

But that's not effective for the processes spawned from run-tests.php. Maybe that should just be added to the $ini_overwrites array here:

php-src/run-tests.php

Line 269 in d34c09f

$ini_overwrites = [