Merge pull request #501 from System-IO-Abstractions/dependabot/nuget/NUnit3TestAdapter-3.15.0

Bump NUnit3TestAdapter from 3.14.0 to 3.15.0

Author: robkeim

System.IO.Abstractions.TestingHelpers.Tests/System.IO.Abstractions.TestingHelpers.Tests.csproj

@@ -47,7 +47,7 @@
 
   <ItemGroup>
     <PackageReference Include="nunit" Version="3.12.0" />
-    <PackageReference Include="NUnit3TestAdapter" Version="3.14.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="3.15.0" />
   </ItemGroup>
 
   <ItemGroup>