Fix csproj for NonUnityBuild

[kekchpek]

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Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• No compiler errors or warnings

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Issue Number

Issue Number: #281

What is the current behavior?

NonUnityBuild/Zenject.sln could not be built

What is the new behavior?

NonUnityBuild/Zenject.sln is built sucsessfully

Does this introduce a breaking change?

• Yes
• No

On which Unity version has this been tested?

N/A

Scripting backend:
N/A

[RimuruDev]

Cool