fix(isoDate): pad a bare-hour timeshift with a colon, not just zeros

[yfwmaniish]

Fixes #2434.

What

`internals.isoDate()` (`lib/types/string.js`) pads a bare-hour UTC timeshift like `+04` before handing the string to `Date()`:

```js
if (/.T.[+-]\d\d$/.test(value)) { // Add missing trailing zeros to timeshift
value += '00';
}
```

That produces `...+0400` — ISO 8601 basic-format offset — glued onto an otherwise extended-format string (`YYYY-MM-DDTHH:mm:ss`). ISO 8601 doesn't allow mixing the two; the correct extended-format offset is `...+04:00`.

This was flagged by @kanongil in review on #2421 (the PR that introduced the line): "You need to add the : as well to make it a proper extended iso date string. As it is, it breaks in Safari." The PR was merged before the fix landed, and #2434 was opened to track it but never addressed.

Also drops the leading .* in the trigger regex, per the same review thread (.test() doesn't need start-anchoring, so it was redundant).

Fix

```js
if (/T.*[+-]\d\d$/.test(value)) { // Add missing separator and trailing zeros to timeshift
value += ':00';
}
```

Testing

Node's own `Date` constructor parses `+0700` and `+07:00` identically, so a test asserting on Joi's converted output (`.toISOString()`) can't distinguish the bug from the fix — I confirmed this empirically before writing the test. Instead, the new test spies on the global `Date` constructor to assert the exact string Joi passes to it.

• Negative control: reverted just the source fix, kept the test — it fails, showing the un-colonized string (`+0700`) reaching `Date()`. Restored.
• Full suite: `lab` — 1824/1824 passing.
• `eslint` clean on both changed files.

[Copilot]

Pull request overview

This pull request fixes string.isoDate() coercion so that ISO 8601 datetimes with a bare-hour UTC offset (e.g. +07) are normalized to the extended offset form (+07:00) before being parsed by Date(), avoiding invalid mixed-format offsets that break stricter parsers (notably Safari).

Changes:

• Update internals.isoDate() normalization to append :00 (extended) instead of 00 (basic) when padding a bare-hour timeshift.
• Simplify the trigger regex by removing the redundant leading .*.
• Add a regression test that spies on the argument passed into Date() to ensure the colonized offset is used.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/types/string.js	Fixes bare-hour offset padding to use +HH:00 (extended format) before calling new Date(value).
test/types/string.js	Adds a regression test that temporarily replaces global.Date to assert the exact string passed to Date().

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