[BUG Report] update fails when Go is installed via mise (standard commands share the same bin directory)

[nao1215]

gup version

v0.28.0

Description (About the problem)

When Go is installed via mise, both standard Go commands (e.g., go, gofmt) and user-installed binaries share the same directory under $GOBIN.
Because of this, gup update tries to update Go’s standard library commands as if they were third-party binaries.

This results in errors such as:

gup:ERROR: [1/7]gofmt: can't install cmd/gofmt:
go: cmd/gofmt@latest: argument must not be a package in the standard library

gup:ERROR: [2/7]go: can't install cmd/go:
go: cmd/go@latest: argument must not be a package in the standard library

Steps to reproduce

1. Install Go via mise.

2. Ensure $GOBIN points to the Go installation directory, e.g.:

   /home/<user>/.local/share/mise/installs/go/1.25.3/bin
   

3. Install gup using go install github.com/nao1215/gup@latest

4. Run:

   gup update
   

5. Observe the error output for cmd/go and cmd/gofmt.

Expected behavior

gup update should automatically ignore or skip binaries that belong to the Go standard library (cmd/go, cmd/gofmt) when they are found in $GOBIN.

Additional details

• OS: Ubuntu (Linux x86_64)
• Go version: 1.25.3 (installed via mise)
• GOBIN: /home/nao/.local/share/mise/installs/go/1.25.3/bin
• gup: v0.28.0

Possible improvements:

• Detect and skip standard Go commands automatically.