.NET: Update version for release

[lokitoth]

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• [ ] Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

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Pull request overview

Updates the .NET NuGet packaging metadata to align with the next release version (1.5.0), ensuring generated package versions and tags reflect the new release line.

Changes:

• Bumped the central NuGet VersionPrefix from 1.4.0 to 1.5.0.
• Updated DateSuffix to 260507 for preview/suffixed package version generation.
• Updated GitTag to 1.5.0 to match the new version prefix.