[PM-5052] Upgrade to .NET 8 (#3461)

* Upgrade to .NET 8

* Linting

* Clean up old JSON deserialization code

* More .NET 8-oriented linting

* Light feedback

* Get rid of old test we don't know the root issue for

* Fix a new test

* Remove now-unnecessary Renovate constraint

* Use Any()

* Somehow a 6.0 tooling config we don't need snuck back in

* Space out properties that always change per release

* Bump a few core packages since the last update

bitwarden_license/src/Scim/Dockerfile

@@ -1,11 +1,11 @@
-FROM mcr.microsoft.com/dotnet/aspnet:6.0
+FROM mcr.microsoft.com/dotnet/aspnet:8.0
 
 LABEL com.bitwarden.product="bitwarden"
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
-        gosu \
-        curl \
+    gosu \
+    curl \
     && rm -rf /var/lib/apt/lists/*
 
 ENV ASPNETCORE_URLS http://+:5000

bitwarden_license/src/Sso/Dockerfile

@@ -1,11 +1,11 @@
-FROM mcr.microsoft.com/dotnet/aspnet:6.0
+FROM mcr.microsoft.com/dotnet/aspnet:8.0
 
 LABEL com.bitwarden.product="bitwarden"
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
-        gosu \
-        curl \
+    gosu \
+    curl \
     && rm -rf /var/lib/apt/lists/*
 
 ENV ASPNETCORE_URLS http://+:5000

bitwarden_license/src/Sso/Utilities/Saml2BitHandler.cs

@@ -167,7 +167,7 @@ static class CommandResultExtensions
 
         foreach (var h in commandResult.Headers)
         {
-            httpContext.Response.Headers.Add(h.Key, h.Value);
+            httpContext.Response.Headers.Append(h.Key, h.Value);
         }
 
         if (!string.IsNullOrEmpty(commandResult.ClearCookieName))