bugfix: Slate breaks on load on Safari < 16.4

[janpaepke]

Description
This is a very serious issue, as it breaks the app using slate on load, not even when interacting with certain parts of slate.

For details see issue below.

Issue
Fixes: #5502

Example

Context
The change makes the check a little bit more verbose but works in exactly the same way: We're testing the user agent for 'Wechat' but exclude 'MacWechat'.

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: e93c885

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR