Remove unsupported SDK targets (#3193)

* yee old sdks (and CI cache too since it's pretty useless)

* also bump deps

* Update src/Discord.Net.Interactions/Discord.Net.Interactions.csproj

Co-authored-by: d4n <dan3436@hotmail.com>

* Update src/Discord.Net.Core/Discord.Net.Core.csproj

Co-authored-by: d4n <dan3436@hotmail.com>

* `.ForEachAsync` => `await foreach`

* remove old targets from .nuspec & update docs

* bump sdk in ws4net provider (probably should deprecate it tho)

---------

Co-authored-by: d4n <dan3436@hotmail.com>

.github/workflows/dotnet.yml

@@ -26,8 +26,6 @@ jobs:
             uses: actions/setup-dotnet@v4
             with:
               dotnet-version: 9.0.x
-              cache: true    
-              cache-dependency-path: "**/packages.lock.json"
 
           - name: Is Tag Build
             if: startsWith(github.ref, 'refs/tags/')