Fix csproj for NonUnityBuild

[kekchpek]

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Pull request checklist

Please check if your PR fulfills the following requirements:

• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been reviewed and added / updated if needed (for bug fixes / features)
• [x] 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)
• [x] 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
• [x] No

On which Unity version has this been tested?

N/A

Scripting backend: N/A

[RimuruDev]

Cool