Bump NSubstitute from 4.3.0 to 4.4.0 in /src (#95)

Bumps NSubstitute from 4.3.0 to 4.4.0.

---
updated-dependencies:
- dependency-name: NSubstitute
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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src/Camelotia.Tests/Camelotia.Tests.csproj

@@ -10,7 +10,7 @@
     </PackageReference>
     <PackageReference Include="FluentAssertions" Version="6.7.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.1" />
-    <PackageReference Include="NSubstitute" Version="4.3.0" />
+    <PackageReference Include="NSubstitute" Version="4.4.0" />
     <PackageReference Include="xunit" Version="2.4.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
       <PrivateAssets>all</PrivateAssets>