Update to .NET 6 Preview 7.

Directory.Build.props

@@ -16,7 +16,7 @@
     <!-- Lots of our dependencies are not strong-named -->
     <NoWarn>$(NoWarn);8002</NoWarn>
     <Nullable>enable</Nullable>
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>10.0</LangVersion>
   </PropertyGroup>
 
   <Import Project="$(RepoRoot)test\Test.Infrastructure\Microsoft.AspNetCore.Testing.props" Condition=" '$(IsTestProject)' == 'true' " />

global.json

@@ -1,12 +1,12 @@
 {
   "tools": {
-    "dotnet": "6.0.100-preview.6.21355.2",
+    "dotnet": "6.0.100-preview.7.21379.14",
     "runtimes": {
       "dotnet": [
-        "6.0.0-preview.6.21352.12"
+        "6.0.0-preview.7.21377.19"
       ],
       "aspnetcore": [
-        "6.0.0-preview.6.21355.2"
+        "6.0.0-preview.7.21378.6"
       ]
     }
   },