Timezone in ISO string not parsed properly

[ThomasRinsma]

Describe the bug
When using fromISO on an string with a timezone in square brackets, a parsing issue is revealed. Specifically, a JavaScript/TypeScript look-up object is used somewhere down the line which uses a regular Object, instead of one with a null-prototype. This means that default Object keys are considered valid, and hence, for example, constructor is (partially) considered a valid timezone:

(pseudocode of likely implementation)

var lookup = {};
if(lookup["constructor"]) { ... } // true

Luckily, later logic seems to fail on these keys, so the only impact appears to be a somewhat confusing error message:

> luxon.DateTime.fromISO("2020-01-01T11:22:33+01:00[constructor]")
DateTime {
  ts: 1742121941768,
  _zone: SystemZone {},
  loc: Locale {
    locale: 'en-US',
    numberingSystem: null,
    outputCalendar: null,
    intl: 'en-US',
    weekdaysCache: { format: {}, standalone: {} },
    monthsCache: { format: {}, standalone: {} },
    meridiemCache: null,
    eraCache: {},
    specifiedLocale: null,
    fastNumbersCached: null
  },
  invalid: Invalid {
    reason: 'unsupported zone',
    explanation: 'the zone "function Object() { [native code] }" is not supported'
  },
  weekData: null,
  c: null,
  o: null,
  isLuxonDateTime: true
}

To Reproduce

var luxon = require("luxon");
console.log(luxon.DateTime.fromISO("2020-01-01T11:22:33+01:00[constructor]"));

Actual vs Expected behavior
The result's invalid.explanation shows:

'the zone "function Object() { [native code] }" is not supported'

while we'd expect:

'the zone "constructor" is not supported'

Desktop (please complete the following information):

• OS: Linux
• Browser: Node
• Luxon version: 3.5.0
• Your timezone: constructor ;)

Additional context
N/A