Millisecond part of ISO String duration being added twice

**Describe the bug**
This may or may not be related to #1652

When using an ISO duration string with a non-integer second value and adding it to a date, the millisecond part gets added twice. For example a duration of "PT0.1S" adds 200ms.

[Example Codepen](https://codepen.io/mrchimp/pen/WNPbBra)

**Expected behavior**
A duration of "PT0.1S" should add 100ms.

**Information**
- Day.js Version v1.11.10
- OS: Ubuntu
- Browser: Chrome 117.0.5938.149
- Time zone: GMT

Start by reproducing the issue with the reported ISO duration "PT0.1S" and the linked CodePen, then trace how ISO durations are parsed and added to dates. Done means the duration adds 100ms rather than 200ms, with a regression test covering the non-integer-second case.

Written by the indexing model from the issue text.