make.bash,bat,rc: use Go 1.20.6 instead of Go 1.17.13

make.bash,bat,rc: use Go 1.20.6 instead of Go 1.17.13

This was missed in the update of the bootstrap toolchain
and should help people who don't set GOROOT_BOOTSTRAP
and instead assume these scripts will find the right one.

For #54265.

Change-Id: I37a0d0976006d13b73df00013780be5abf202e91
Reviewed-on: https://go-review.googlesource.com/c/go/+/512275
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>