Fix heading format in whats-new.md

[VeronicaSnyk]

Correct the heading format for consistency.

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Note

Low Risk
Single-line documentation heading change with no functional or security impact.

Overview
Updates the top-level heading in discover-snyk/whats-new.md from What's new? to What's new, dropping the trailing question mark so the title matches other documentation page headings.

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[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

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✅	Code Security	0	0	0	0	0 issues

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