CustomParseFormat does not parse UTC offset in strict mode

**Describe the bug**
```
// From CustomParseFormat documentation, assertion passes:
assert(dayjs("05/02/69 1:02:03 PM -05:00", "MM/DD/YY H:mm:ss A Z").isValid())

// Same example but with strict=true, assertion fails:
assert(dayjs("05/02/69 1:02:03 PM -05:00", "MM/DD/YY H:mm:ss A Z", true).isValid())
```

**Expected behavior**
Both should pass

**Information**
- Day.js Version: 1.11.13
- OS: Windows 10
- Browser: NodeJs v20.17.0
- Time zone: Europe/Warsaw UTC+2

Start with the reported CustomParseFormat reproduction and compare the non-strict and strict parsing paths for the `Z` UTC offset. Add a regression test for `05/02/69 1:02:03 PM -05:00` with strict mode, and consider the issue done when both assertions pass.

Written by the indexing model from the issue text.