[c#] Fix Table __vector_as_array correct len calc (#8911)

* fix for https://github.com/google/flatbuffers/issues/8759
__vector_as_array<T> calling ByteBuffer.ToArray<T> with the length in bytes by multiplying len with ByteBuffer.Sizeof<T> and FlatBuffersExampleTests extended to call GetVectorOfLongsArray/GetVectorOfDoublesArray which failed without the fix

* first try to repair build-dotnet-windows

* syntax error fixed

* Update solution creation command in build workflow

add --format sln to the dotnet new command, maybe it is currently creating a .slnx instead?

.github/workflows/build.yml

@@ -197,8 +197,7 @@ jobs:
         configuration: [
           '',
           '-p:UnsafeByteBuffer=true',
-          # Fails two tests currently.
-          #'-p:EnableSpanT=true,UnsafeByteBuffer=true'
+          '-p:EnableSpanT=true,UnsafeByteBuffer=true'
           ]
     steps:
     - uses: actions/checkout@v6
@@ -209,7 +208,7 @@ jobs:
     - name: Build
       run: |
         cd tests\FlatBuffers.Test
-        dotnet new sln --force --name FlatBuffers.Test
+        dotnet new sln --force --name FlatBuffers.Test --format sln
         dotnet sln FlatBuffers.Test.sln add FlatBuffers.Test.csproj
         dotnet build -c Release ${{matrix.configuration}} FlatBuffers.Test.sln
     - name: Run net6.0