Fix typo in design rule hint message

[jahvi]

Description

Change text in design rule hint message from "Search strings are either normal strings or regular exceptions (PCRE)" to "Search strings are either normal strings or regular expressions (PCRE)".

Fixed Issues (if relevant)

1. Hint mistake in english language #8958: Hint mistake in english language

Manual testing scenarios

1. Login to backend
2. Navigate to Content > Configuration
3. Click "Edit" in Global scope.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

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