Move gitea-vet to use go tool (#35878)

Add it as a [tool
dependency](https://go.dev/doc/modules/managing-dependencies#tools),
eliminating the need for `build.go`.

.github/labeler.yml

@@ -51,7 +51,6 @@ modifies/internal:
           - ".github/**"
           - ".gitea/**"
           - ".devcontainer/**"
-          - "build.go"
           - "build/**"
           - "contrib/**"