.NET: Version bump for .net release

[westey-m]

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• The code builds clean without any errors or warnings
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Pull request overview

Bumps the centralized .NET NuGet package version metadata used across the dotnet/ build so upcoming package builds/pack operations produce the new version.

Changes:

• Update the central VersionPrefix from 1.13.0 to 1.14.0.
• Update the DateSuffix used in preview/suffixed package versions to 260721.
• Update the GitTag value to 1.14.0.