x/build/cmd/release: update to FreeBSD-[amd64|386]-11_4 builder for 1.17 Beta

[cagedmantis]

The cmd/release command is currently configured to use the freebsd-{amd64,386}-11_2 builders for the freebsd release targets.

FreeBSD 11.2 will not be supported by the time Go 1.17 is released. We should use FreeBSD 11.4 builders during the release.

/cc @golang/release

[gopherbot]

Change https://golang.org/cl/313070 mentions this issue: dashboard: make FreeBSD 11.4 and 12.2 builders the default

[dmitshur]

Using the latest "patch" release of the oldest "major" release of FreeBSD that we support for issuing Go 1.17 releases seems consistent with what we've done before, and SGTM.

[gopherbot]

Change https://golang.org/cl/315889 mentions this issue: cmd/release: start using the FreeBSD 11.4 builder for Go 1.17