Downgrade go runtime to 1.16 for macOS AppRTC tests.

Starting from Go 1.17, modules are the default and cannot be disabled.
This requires a change in the GitHub repositury [1].

As a stopgap solution, this CL moves Go back to 1.16 and disables
modules [2].

[1] - https://github.com/webrtc/apprtc/tree/master/src/collider
[2] - https://go.dev/blog/go116-module-changes

No-Presubmit: True
Bug: webrtc:14342
Change-Id: Idd03639588bc03497a78f0cef350daebf3b2f1d9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/271481
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37760}

rtc_tools/testing/build_apprtc.py

@@ -55,6 +55,7 @@ def main(argv):
     golang_env = os.environ.copy()
     golang_env['GOROOT'] = go_root_dir
     golang_env['GOPATH'] = golang_workspace
+    golang_env['GO111MODULE'] = 'off'
     collider_out = os.path.join(
         golang_workspace, 'collidermain' + utils.GetExecutableExtension())
     subprocess.check_call(

rtc_tools/testing/golang/mac/go.tar.gz.sha1

@@ -1 +1 @@
-94422c2571e68e7725b9fb878c37e7de47a2351a
+e13521f5d61465fe873371b266bc3ceafcb13562