Bump Argon from 0.14.0 to 0.15.0 in /src

Bumps [Argon](https://github.com/SimonCropp/Argon) from 0.14.0 to 0.15.0.
- [Release notes](https://github.com/SimonCropp/Argon/releases)
- [Commits](https://github.com/SimonCropp/Argon/commits/0.15.0)

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

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

src/Tests/Tests.csproj

@@ -7,7 +7,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
     <PackageReference Include="Microsoft.AspNetCore.TestHost" Version="8.0.0" />
-    <PackageReference Include="Argon" Version="0.14.0" />
+    <PackageReference Include="Argon" Version="0.15.0" />
     <PackageReference Include="MarkdownSnippets.MsBuild" Version="26.0.1" PrivateAssets="all" />
     <PackageReference Include="Verify.DiffPlex" Version="2.3.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6" PrivateAssets="all" />