Use X509Certificate2 constructor instead of Import (SYSLIB0026)

[MiguelDomingues]

Summary

Import is marked as obsolete (SYSLIB0026):

'X509Certificate.Import(byte[])' is obsolete: 'X509Certificate and X509Certificate2 are immutable. Use the appropriate constructor to create a new certificate.'

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-security, @vcsjones

[learn-build-service-prod]

Learn Build status updates of commit 2cae909:

✅ Validation status: passed

File	Status	Preview URL	Details
snippets/csharp/System.Security.Cryptography.X509Certificates/PublicKey/Overview/certinfo.cs	✅Succeeded	View

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