This build variant uses `db-contrib-tool` to pull down existing branch binaries that may be newer than the server commit that it is building from. It then builds from that commit with a new git-tag to simulate a higher-version release, and runs it in a multiversion cluster with the existing branch binaries to try and ensure that new release tags don't break tests.

However, because the existing branch binaries may actually be newer than the version it is building from, it may be running jstests that are out-of-date relative to the binaries it pulled. For example, if a failpoint is renamed from "name1" to "name2" in a commit between the one being tested and the one the existing-branch-builds are from, the pulled binaries will expect "name2" but the jstests will use "name1", therefore breaking the tests.