unix/linux: update Dockerfile to Go 1.17beta1

Running `GOOS=linux GOARCH=amd64 ./mkall.sh` produces no changes, as
expected.

Change-Id: I09ec5243376fe76792d2b5e4984d8e2409dc7ce3
Reviewed-on: https://go-review.googlesource.com/c/sys/+/327729
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Author: tklauser

unix/linux/Dockerfile

@@ -21,9 +21,9 @@ RUN git clone --branch v5.12 --depth 1 https://kernel.googlesource.com/pub/scm/l
 RUN git clone --branch release/2.33/master --depth 1 git://sourceware.org/git/glibc.git
 
 # Get Go
-ENV GOLANG_VERSION 1.16.3
+ENV GOLANG_VERSION 1.17beta1
 ENV GOLANG_DOWNLOAD_URL https://golang.org/dl/go$GOLANG_VERSION.linux-amd64.tar.gz
-ENV GOLANG_DOWNLOAD_SHA256 951a3c7c6ce4e56ad883f97d9db74d3d6d80d5fec77455c6ada6c1f7ac4776d2
+ENV GOLANG_DOWNLOAD_SHA256 a479681705b65971f9db079bfce53c4393bfa241d952eb09de88fb40677d3c4c
 
 RUN curl -fsSL "$GOLANG_DOWNLOAD_URL" -o golang.tar.gz \
     && echo "$GOLANG_DOWNLOAD_SHA256  golang.tar.gz" | sha256sum -c - \