The `gmtime()` function returns the given epoch timestamp (or now,
if omitted) as a dictionary containing broken-down date and time
information interpreted as UTC time.

-- Testcase --
{%
	let t = time();
	let d1 = gmtime();
	let d2 = gmtime(1647953502);

	// assert that localtime without epoch returns the current time
	let c = timegm(d1);
	assert(c >= t && c <= t + 5, "gmtime() result does not match time()");

	// dump fixed time and check expected output
	printf("%.J\n", d2);
%}
-- End --

-- Expect stdout --
{
	"sec": 42,
	"min": 51,
	"hour": 12,
	"mday": 22,
	"mon": 3,
	"year": 2022,
	"wday": 2,
	"yday": 81,
	"isdst": 0
}
-- End --