cmd/go: env should report GOPACKAGESDRIVER

[adonovan]

Most bug reports include the output of go env, but this does not include GOPACKAGESDRIVER since this variable does not affect the go command. But it does have a big influence on many other tools, such as gopls, vulncheck, deadcode, and so on, so we should include it in bug reports too.

[gabyhelp]

Related Issues

• x/tools/go/packages: document GOPACKAGESDRIVER #34341 (closed)
• x/tools/gopls: ignore gopackagesdriver in PATH #66041
• cmd/go: `go env` does not show GODEBUG #65777 (closed)
• cmd/go: add a way to query for non-defaults in the env #34208 (closed)
• cmd/bug: Exclude GOPRIVATE from go bug by default #73099 (closed)

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[dmitshur]

CC @golang/command-line.