Wrong diagnostics for `_specialize` attribute

[kimdv]

Description

#1549 (comment)

https://github.com/apple/swift-syntax/blob/00b0ce7017707525b24d0d577277bdebbbc0c91a/CodeGeneration/Sources/SyntaxSupport/AttributeNodes.swift#L801

Steps to Reproduce

No response

[ahoppen]

Tracked in Apple’s issue tracker as rdar://108655870