The omnisharp server will use the dotnet (NET6) runtime to run the server. To run the server using the Mono runtime,
use the omnisharp_mono server instead (this requires the omnisharp-mono package to be installed).
Note: The omnisharp_mono server configuration doesn't exist in lspconfig but is provided by mason-lspconfig.
This is done in order to separate the .NET and Mono variants, making both easily accessible.
local lspconfig = require "lspconfig"
lspconfig.omnisharp_mono.setup {}