Bump Microsoft.AspNetCore.Mvc.Testing from 5.0.17 to 7.0.3 in /backend

Bumps [Microsoft.AspNetCore.Mvc.Testing](https://github.com/dotnet/aspnetcore) from 5.0.17 to 7.0.3.
- [Release notes](https://github.com/dotnet/aspnetcore/releases)
- [Changelog](https://github.com/dotnet/aspnetcore/blob/main/docs/ReleasePlanning.md)
- [Commits](dotnet/aspnetcore@v5.0.17...v7.0.3)

---
updated-dependencies:
- dependency-name: Microsoft.AspNetCore.Mvc.Testing
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/RossyntBackendIntegrationTest/RossyntBackendIntegrationTest.csproj

@@ -10,8 +10,8 @@
 
     <ItemGroup>
         <PackageReference Include="AutoFixture" Version="4.17.0" />
-        <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="6.0.13" Condition="'$(TargetFramework)' == 'net6.0'" />
-        <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="7.0.2" Condition="'$(TargetFramework)' == 'net7.0'" />
+        <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="7.0.3" Condition="'$(TargetFramework)' == 'net6.0'" />
+        <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="7.0.3" Condition="'$(TargetFramework)' == 'net7.0'" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.1" />
         <PackageReference Include="NUnit" Version="3.13.3" />
         <PackageReference Include="NUnit3TestAdapter" Version="4.3.1" />