build: rename scoop to charm-gum (#504)

gum conflicts with another tool, even if it is in our own bucket, this
still makes it difficult to install.

the official scoop for gum is also called charm-gum, so I think this
should work better.

refs charmbracelet/scoop-bucket#7

.goreleaser.yml

@@ -4,6 +4,7 @@ includes:
 
 variables:
   main: "."
+  scoop_name: charm-gum
   description: "A tool for glamorous shell scripts"
   github_url: "https://github.com/charmbracelet/gum"
   maintainer: "Maas Lalani <maas@charm.sh>"