cicd: add script to edit module for nightly

This script should automate editing the clair module so that it builds
against claircore's main branch. The idea is to run this in a CI job,
build the resulting code, and then throw away the modifications.

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

.github/script/nightly-module.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+set -e
+: ${CLAIRCORE_BRANCH:=main}
+: ${GO_VERSION:=1.17}
+test "${#GO_VERSION}" -gt 4 && GO_VERSION=${GO_VERSION%.*}
+
+cd $(git rev-parse --show-toplevel)
+echo '#' "$(go version)"
+go mod edit "-go=${GO_VERSION}"\
+	"-replace=github.com/quay/claircore=github.com/quay/claircore@${CLAIRCORE_BRANCH}"
+git diff
+test -d vendor && rm -rf vendor
+go mod tidy