Run upstream tests on images in CI here

This runs upstream's `dist test` which is roughly `go test std cmd`.

Author: tianon

.test/config.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# https://github.com/docker-library/official-images/blob/3bc6a70175d4e1da2080b86415e6f3c8eb2c6af3/test/config.sh
+
+imageTests[golang]+='
+	go-dist-test
+'

.test/tests/go-dist-test/run.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+set -Eeuo pipefail
+
+image="$1"
+
+args=(
+	# respond better to SIGINT/SIGTERM
+	--init --interactive
+
+	# Go has some tests that are very picky about DNS resolution
+	--dns 8.8.8.8
+	--dns 8.8.4.4
+)
+
+cmd=(
+	# the "dist" tool doesn't query Go for GOROOT and expects it to be set explicitly
+	sh -xec 'GOROOT="$(go env GOROOT)" && export GOROOT && exec "$@"' --
+
+	# ideally this would just be "go tool dist test" but it isn't built by default (because most users don't need it)
+	go run cmd/dist test
+)
+
+case "$image" in
+	*alpine*)
+		# Alpine needs a few extra dependencies installed for the tests to run/pass
+		# gcc/libc-dev: cgo-related tests
+		# iproute2-minimal: BusyBox's "ip" isn't enough for tests that need to shell out to "ip" for various env setup
+		cmd=( sh -xec 'apk add --no-cache gcc libc-dev iproute2-minimal && exec "$@"' -- "${cmd[@]}" )
+		# for some reason, running the tests on Alpine needs NET_ADMIN (but not on Debian 🤔)
+		args+=( --cap-add NET_ADMIN )
+		;;
+
+	*windows* | *nanoserver*)
+		echo >&2 "note: tests do not run successfully in a Windows container yet (https://github.com/docker-library/golang/issues/552#issuecomment-2658011431)"
+		exit 0
+		;;
+esac
+
+if [ -t 0 ] && [ -t 1 ]; then
+	# let Ctrl+C DTRT if we're at a TTY
+	args+=( --tty )
+fi
+
+docker run --rm "${args[@]}" "$image" "${cmd[@]}"