docs: fix #47146 – improve email validation regex to prevent invalid formats

[Gurry-12]

What this PR does:

This PR updates the email validation regex in the How to verify that strings are in valid email format article to address an issue where invalid characters (like commas) were being accepted.
Problem:

The current regex pattern:

^[^@\s]+@[^@\s]+.[^@\s]+$

allows email addresses like surname123@gmail.,com, which are structurally invalid.
Fix:

Replaced the regex pattern and its explanation with a more accurate expression:

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$

This change:

Restricts characters in the local and domain parts to common valid characters.

Ensures the TLD has at least two alphabetical characters.

Still remains readable and practical for general validation.

Related issue:

Fixes #47146

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Internal previews

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docs/standard/base-types/how-to-verify-that-strings-are-in-valid-email-format.md	How to verify that strings are in valid email format

[Gurry-12]

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