Cannot set thresholds on a new locale

**Describe the bug**
Trying to create a new locale and pass in thresholds such that '23 hours ago' would be '23h' and anything less than 24hours would not show up as days.

Code
`import dayjs from '@/js/be/dayJSPlugins.js';

const localeObject = {
name: 'en-segment',
relativeTime: {
future: 'in %s',
past: '%s',
s: '%ds',
m: '%dm',
mm: '%dm',
h: '%dh',
hh: '%dh',
d: '%dd',
dd: '%dd',
M: '%dM',
MM: '%dM',
y: '%dy',
yy: '%dy',
},
};

export function getRelativeTime(timestamp) {
dayjs.locale('en-segment', localeObject);
delete relativeTime.$i // this allow plugin to be installed again
dayjs.extend(relativeTime, {
rounding: Math.floor,
thresholds: [
{ l: 's', r: 60 },
{ l: 'm', r: 60 },
{ l: 'h', r: 24 },
],
});

return dayjs.unix(timestamp).fromNow();
}
`

**Information**
- Day.js Version 1.10.6
- OS: MacOS Catalina
- Browser Chrome 93
- Time zone: GMT-07:00 DST (Pacific Daylight Time)

Start by reading js/be/dayJSPlugins.js and the relativeTime plugin setup shown in the report, then reproduce the custom locale with the supplied thresholds. Check how the plugin handles thresholds after installation and verify that times under 24 hours remain in hours while 23 hours is formatted as 23h.

Written by the indexing model from the issue text.