Diff names when listing workspace packages due to not finding local package

[JordanMartinez]

I ran the following:

$ npx spago build -p untyped-lambda-calculus
Reading Spago workspace configuration...

❌ Selected package untyped-lambda-calculus was not found in the local packages.
Available packages:
  untyped-lamda-calculus

The issue was that I was missing the b in lambda in my spago.yaml file's package.name field.

-untyped-lamda-calculus
+untyped-lambda-calculus

It would be helpful if we diff'd the names to help one realize that they misspelled something.

Relates somewhat to #985.