tz() produces incorrect time when passing in milliseconds since the epoch near DST boundary.

[jwalton]

Describe the bug

const dayjs = require('dayjs');
dayjs.extend(require('dayjs/plugin/utc'));
dayjs.extend(require('dayjs/plugin/timezone'));

// On March 13, 2022 in America/Montreal, at 2:00am, we roll the time back by 1 hour.
// This is the exact millisecond when that happens:
const dstBoundary = 1647154800000;

// This should obviously be true, and it is.
console.log(dayjs.tz(dstBoundary - 1, 'America/Montreal').valueOf() === dstBoundary - 1);

// This should also obviously be true, but it is false.  :(
console.log(dayjs.tz(dstBoundary, 'America/Montreal').valueOf() === dstBoundary);

Expected behavior

When explicitly setting the time as a value in ms since the epoch, dayjs should not change the time we set, but here it does, rewinding time by one hour. 1647154800000 and 1647151200000 are two very different times.

Information

• Day.js Version: v1.10.8
• OS: MacOS
• Browser: node v16.14.0
• Time zone: America/Montreal