... I am wondering if it is practical to make a change analogous to the one in this PR to improve the diagnostics when the feature isn't supported in the user's LangVersion: https://github.com/dotnet/roslyn/pull/54797/files

Originally posted by @RikkiGibson in #56200 (comment)

Update the diagnostic reported for conversion of lambda expression to base type to suggest using -langversion:10 or higher.

Relates to test plan #52192