Use github backend for golangci-lint in mise

The default aqua backend's nested platform-specific directory
structure was not being included in mise env PATH output on
cache misses in CI, causing precious lint to fail.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: oschwald

mise.toml

@@ -2,7 +2,7 @@
 go = "latest"
 hugo = "latest"
 node = "latest"
-golangci-lint = "latest"
+"github:golangci/golangci-lint" = "latest"
 "github:houseabsolute/precious" = "latest"
 "npm:prettier" = "latest"