Update csharp target framework to net9.0

Author: oscarsj

.github/workflows/swift.yml

@@ -48,12 +48,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: ./swift/actions/build-and-test
-  build-and-test-linux:
-    if: github.repository_owner == 'github'
-    runs-on: ubuntu-24.04
-    steps:
-      - uses: actions/checkout@v4
-      - uses: ./swift/actions/build-and-test
   qltests-macos:
     if: ${{ github.repository_owner == 'github' && github.event_name == 'pull_request' }}
     needs: build-and-test-macos

csharp/ql/integration-tests/all-platforms/autobuild/Files.expected

@@ -1,3 +1,3 @@
 | Program.cs:0:0:0:0 | Program.cs |
-| obj/Debug/net5.0/.NETCoreApp,Version=v5.0.AssemblyAttributes.cs:0:0:0:0 | obj/Debug/net5.0/.NETCoreApp,Version=v5.0.AssemblyAttributes.cs |
-| obj/Debug/net5.0/autobuild.AssemblyInfo.cs:0:0:0:0 | obj/Debug/net5.0/autobuild.AssemblyInfo.cs |
+| obj/Debug/net9.0/.NETCoreApp,Version=v5.0.AssemblyAttributes.cs:0:0:0:0 | obj/Debug/net9.0/.NETCoreApp,Version=v5.0.AssemblyAttributes.cs |
+| obj/Debug/net9.0/autobuild.AssemblyInfo.cs:0:0:0:0 | obj/Debug/net9.0/autobuild.AssemblyInfo.cs |

csharp/ql/integration-tests/all-platforms/autobuild/autobuild.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net5.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>