Replace SHA-1 fingerprints with SHA-256 fingerprints

[dtivel]

SHA-1 fingerprints should not be used. Use SHA-256 fingerprints instead. This is for SDL compliance.

From https://github.com/search?q=repo%3ANuGet%2FNuGetGallery%20SHA-1&type=code

• NuGetGallery/src/NuGetGallery/Views/Packages/_ValidationIssue.cshtml

  Line 56 in 27cbca3

  The package was signed, but the signing certificate (SHA-1 thumbprint @typedIssue.Sha1Thumbprint) is not associated with your account.

• NuGetGallery/src/NuGetGallery.Core/Extensions/ValidationIssueExtensions.cs

  Line 55 in 27cbca3

  return $"The package was signed, but the signing certificate {(certIssue != null ? $"(SHA-1 thumbprint {certIssue.Sha1Thumbprint})" : "")} is not associated with your account. You must register this certificate to publish signed packages. [Read more...](https://aka.ms/nuget-signed-ref)";

• NuGetGallery/tests/NuGetGallery.Facts/Infrastructure/Mail/MarkdownMessageServiceFacts.cs

  Line 1375 in 27cbca3

  return $"The package was signed, but the signing certificate (SHA-1 thumbprint {certIssue.Sha1Thumbprint}) is not associated with your account. You must register this certificate to publish signed packages. [Read more...](https://aka.ms/nuget-signed-ref)";

• NuGetGallery/tests/NuGetGallery.Facts/Infrastructure/Mail/MarkdownMessageServiceFacts.cs

  Line 2318 in 27cbca3

  return $"The package was signed, but the signing certificate (SHA-1 thumbprint {certIssue.Sha1Thumbprint}) is not associated with your account. You must register this certificate to publish signed packages. [Read more...](https://aka.ms/nuget-signed-ref)";

[joelverhagen]

Related: #9523.

[mariaghiondea]

Related internal item: Task 2046665: Use approved crypto libraries for the supported platform