gpm: deprecate

[chenrui333]

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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go get is no longer supported outside of a module in the legacy GOPATH mode (that is, with GO111MODULE=off). Other build commands, such as go build and go test, will continue to work indefinitely for legacy GOPATH programs.

https://tip.golang.org/doc/go1.22

• relates to go 1.22.0 #157782
• Compatibility with future Go versions pote/gpm#93