Bump NunitXml.TestLogger from 3.1.15 to 3.1.20

Bumps [NunitXml.TestLogger](https://github.com/spekt/nunit.testlogger) from 3.1.15 to 3.1.20.
- [Release notes](https://github.com/spekt/nunit.testlogger/releases)
- [Changelog](https://github.com/spekt/nunit.testlogger/blob/master/CHANGELOG.md)
- [Commits](spekt/nunit.testlogger@v3.1.15...v3.1.20)

---
updated-dependencies:
- dependency-name: NunitXml.TestLogger
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Rdmp.Dicom.Tests/Rdmp.Dicom.Tests.csproj

@@ -50,7 +50,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
-    <PackageReference Include="NunitXml.TestLogger" Version="3.1.15" />
+    <PackageReference Include="NunitXml.TestLogger" Version="3.1.20" />
   </ItemGroup>
   <ItemGroup>
     <None Update="TestDatabases.txt">