dhall-lsp-server needs better test coverage

[sjakobi]

For example for the type-on-hover functionality we currently have only two tests:

dhall-haskell/dhall-lsp-server/tests/Main.hs

Lines 39 to 40 in 619788f

	getValue typeContent `shouldBe` "Type"
	getValue functionContent `shouldBe` "\8704(_isAdmin : Bool) \8594 { home : Text, name : Text }"

(This is a follow-up to #1510.)